Durability of vapor-permeable waterproof textile materials used in sailing protective apparel

Abstract

Vapor-permeable waterproof textiles (VPWTs) are used in sailing apparel to protect wearers from weather and water exposure. They must also withstand knocks and abrasion. Failure of fabric waterproofing results in water intrusion, reduced thermal protection and potentially hypothermia. There are no standard methods for testing the waterproof durability of fabrics in these conditions.

To evaluate waterproofing durability, we simulated high levels of wear on leading commercially available VPWT assemblies through mechanical treatment in wet conditions. To compare fabrics on multiple performance characteristics, we developed a Total Durability Penalty index associated with leaks and ruptures, weighted by failure pressure.

The experiment revealed significant differences in VPWT deterioration under mechanical treatment. We determined that the mass per unit area and thickness of VPWT fabrics are positively correlated with pressure at leakage; that rupture is significantly and negatively associated with the mass per unit area and thickness of the inner and outer layers of fabric; and leakage pressure is positively correlated with the same parameters. These results show that it is important to consider wear conditions when assessing the long-term performance attributes of protective clothing assemblies.

Keywords

vapor-permeable waterproof textiles sailing apparel waterproof durability testing toughness materials performance

Vapor-permeable waterproof textiles (VPWTs) are widely used in modern outdoor apparel and sportswear. Their primary functions are to protect the wearer from environmental factors, such as wind, cold and rain, and to allow the diffusion of water vapor from the microclimate under the garment to the outside environment^1,2 while remaining impervious to external liquids, such as rainwater.^3–5

VPWTs are sometimes classified as waterproof, rain repellent or showerproof. Waterproof textiles give the most protection from water penetration; rain-repellent materials should withstand “fairly heavy” rain, while showerproof materials offer protection only against light drizzle.⁵

Textiles can be made vapor-permeable and waterproof using densely woven fabrics, membranes or coatings applied to various substrates, mainly fabrics.^5,6

Densely woven fabrics

Densely woven VPWTs are constructed either from natural hydrophilic fibers and yarns or synthetic filament yarns in micro-denier yarn counts. The aim of constructing waterproof fabrics from these yarns is to make the inter-fiber and inter-yarn pores and voids small enough to be impenetrable to water droplets. When a hydrophilic natural fiber is used (e.g. cotton), it is combed to improve fiber regularity, reduce fiber protrusion from the yarn surface and to increase fiber alignment to the yarn axis, all of which reduces inter-fiber and inter-yarn pore size. To further reduce the fabric structural voids, the yarn is generally woven using an Oxford weave (a plain weave with two threads acting together in the warp to give minimum crimp in the weft), again ensuring that the fibers are as parallel as possible to the surface of the fabric. On wetting, the cotton fibers swell transversely, further reducing pore size and increasing the water pressure needed for penetration; therefore, the fabric becomes waterproof without additional water-repelling finish or treatment. The disadvantage of these types of fabrics is that they cannot maintain their waterproof characteristics for long (a maximum of 20 minutes in one study⁷), and therefore are not recommended for use in heavy or prolonged rain.^2,5

Densely woven synthetic microfilament fabrics are constructed from individual filaments with diameter less than 10 µm. These microfilaments are usually made from polyamide or polyester, which are hydrophobic with very low moisture regain. Because these synthetic fibers can be produced with smooth surfaces and small diameters, the inter-fiber and inter-yarn pores and fabric structural voids can be significantly smaller than water droplets, but unlike the cellulosic fibers they do not benefit from wetting and swelling and are not truly waterproof.^2,5

Membranes

Membranes are thin films made from polymeric material engineered for very high resistance to liquid water penetration, yet allow the passage of water vapor. A typical membrane is only around 10 µm thick and, therefore, in practical applications is laminated to a conventional textile fabric substrate to provide mechanical strength and durability. Vapor-permeable waterproof membranes are either microporous or hydrophilic.⁵

A microporous membrane is a thin film of expanded polytetrafluoroethylene (PTFE) polymer claimed to contain 1.4 billion pores per square centimeter. The pore size of a microporous membrane is 2–3 µm, significantly smaller than the smallest water drop (100 µm) and larger than a water vapor molecule (40 × 10⁻⁶µm). The hydrophobic nature of the polymer used and small pore size requires very high liquid water pressure to cause its penetration, yet allows water vapor to pass through the membrane,^5,6 and therefore these membranes are considered “breathable”.

Hydrophilic membranes are thin films of chemically modified polyester or polyurethane that incorporate up to 40% polyethylene oxide by weight. They contain no pores, so are sometimes referred to as non-poromeric. Water vapor diffuses by solid-state diffusion through these membranes in large quantities in comparison to microporous membranes.^5,6

These types of membranes can be incorporated into textile material assemblies using five methods, as described below.

A laminate assembly of membrane and outer fabric (Figure 1(a)) is created when the membrane is laminated to the inner side of the outer fabric to produce a two-layer system and an inner layer/lining is added.^5–7
Figure 1.
Methods of incorporating membranes: (a) laminate of membrane and outer fabric; (b) line or insert pressing; (c) laminate of membrane and lining fabric; (d) laminate of outer fabric, membrane and lining; (e) eaminate of membrane and outer fabric (membrane outside).

The membrane can also be laminated to a lightweight substrate or scrim and then loosely inserted between the outer fabric and the inner layer. The three material layers (outer, laminate and lining) are then joined with concealed seams (Figure 1(b)).^5,6

The membrane can be attached to the inner layer of material facing the outer layer fabric, which protects the membrane from direct ambient exposure. This functional layer is then incorporated into the garment as a separate layer independent of the outer fabric (Figure 1(c)).^5–7

Laminating an outer fabric, membrane and lining produces a three-layer system, which gives a less tactile handle and lower drape than the other methods (Figure 1(d)).^5–7

In the latest VPWTs, the membrane is exposed to the outside environment. For example, OutDry™ Extreme is constructed with a durable waterproof microporous membrane directly fused to the outside of the outer shell and soft, wicking fabric inside (Figure 1(e)).⁸

Coatings

Coatings consist of a layer of polymeric material applied to the inner side of the outer fabric. The most widely used coating polymers are polyurethane, poly-tetrafluoroethylenes, acrylics and polyamino acids. Polyurethane is the most widely used coating polymer for contemporary outdoor winter apparel and sportswear because of its durability, flexibility and its ability to suit different clothing applications. The coatings are microporous or hydrophilic and have similar performance attributes to the corresponding membrane types. Hydrophilic coatings are based on chemically modified polyurethane by incorporating polyvinyl alcohols and polyethylene oxides.^5,6

Assessment of garment performance

To assess textiles’ waterproofness and vapor permeability characteristics, as well as the durability of these attributes, resistance to water penetration and water vapor permeability are measured both in a non-treated state and after the application of wear treatment (such as cyclic flexing or abrasion).⁹ However, at present there is no standard method for rating fabrics as “waterproof”.

In previous studies, researchers assessed the vapor permeability and resistance to water penetration of VPWTs after multiple flexing cycles on a Crumple-flex machine and after cyclic stretching treatments.^10,11 In 2008, Padleckiene et al.¹⁰ investigated the water vapor permeability and water penetration resistance of two VPWTs after cyclic stretching treatments applied by a universal testing machine. In this study, one material had three layers – 100% polyester outer fabric, a hydrophilic polyurethane membrane and 100% polyester knitted lining; the second consisted of 100% polyamide plain woven fabric with an inner polyurethane microporous coating. Cyclic stretching was carried out using the fixed elongation method and materials were stretched by 15%, 20% and 25% for 100, 180 and 260 stretching cycles, respectively. The results indicated that water vapor permeability increased with the number of stretching cycles due to membrane damage. Both materials’ resistance to water penetration decreased as the number of stretching cycles increased. The methods used, however, did not simulate the multi-directional and multi-factorial wear and tear the fabrics experience in practical use.

In 2010, Padleckiene and Petrulis¹¹ investigated the mechanical damage to VPWT coatings from various numbers of flexing cycles. Four commercially available VPWTs comprised of woven fabrics with polyurethane coatings on their inner sides were selected. Flexing fatigue resistance tests were carried out on a crumple tester M262 (SDL International Ltd). The fabrics were subjected to 30,000, 60,000, 90,000 and 120,000 cycles, and a hydrostatic head pressure tester was used to examine the waterproofness of coatings after flexing. The results demonstrated that the water penetration resistance of the materials decreased by 85% as the number of flexing cycles increased from 30,000 to 120,000, with water penetration resistance of all VPWTs being 150 kPa before mechanical treatment and below 40 kPa after 120,000 cycles after the treatment.¹¹

In static water column testing, a height of 700 cm H₂O (68 kPa⁹) is generally regarded as the absolute minimum water pressure a textile material must withstand to be termed waterproof or resistant to water penetration.⁹ Some manufacturers use in-house systems based on static column testing to rate the waterproof characteristics of their textile materials. Typically, a 1-inch-diameter tube is placed vertically over a piece of material. The tube is filled with water, and the height of the water column in mm or cm is recorded when leakage appears and is reported as the fabric’s waterproofness rating. A fabric that withstands a water column height of 20,000 mm has a rating of 20,000 mm H₂O, equivalent to 196 kPa,¹² and is widely accepted as “waterproof” by manufacturers.¹² However, static column testing is not a standardized method and thus ratings based on it cannot be considered universal measures.^13,14

Further, sail clothing manufacturers’ waterproof testing for outdoor textiles commonly consists of hydrostatic head testing of the laminated textile assembly. While these test methods provide a good indication of the water pressure that a textile assembly is able to withstand before leaking in an unworn state, they do not necessarily indicate how the textile assembly will maintain this waterproofness through the active life of the product. Some manufacturers wash the fabrics multiple times and then repeat the hydrostatic tests¹⁵; these methods provide an indication of the durability of the waterproofness of the product with respect to washing, but do not simulate the levels of wear experienced during practical use in offshore sailing. There is currently no standard method that simulates the wear to which offshore sailing foul weather gear is subjected; the method developed for this study provides a novel approach to practical wear performance and durability assessment.

Waterproof textiles used in sailing clothing

Fabrics for protective sailing garments are manufactured to be waterproof, windproof and provide cold weather protection. They must also be durable enough to withstand the knocks and abrasion encountered during sailing and to remain waterproof for a reasonable length of time and after repeated washing or cleaning. Failure of the waterproofing results in water intrusion into garments, reduced thermal protection and potentially hypothermia. Knocks and abrasion are caused by fabrics contacting fittings and fixtures, and rubbing against abrasive surfaces, such as grip-enhanced decks. In addition, offshore sailing apparel is subjected to mechanical impacts from objects contained in pockets and inside clothing, such as personal locator beacons, knives and other tools. These objects can further damage the waterproof function of fabrics.

Broad approach

Existing studies, reviewed in the Assessment of garment performance section, were carried out using methods such as the application of wear through limited flexing or rubbing actions that do not fully simulate the multi-modal and high levels of practical wear in offshore sailing conditions. To overcome some of the limitations of previous studies in determining waterproof performance, the present study was designed to simulate in-field wear by exposing materials to objects, abrasion and impacts over time in wet conditions.

Materials and methods

The authors developed an experimental methodology for evaluating the durability of waterproofness of VPWTs, involving simulating high levels of wear through the application of mechanical wear treatment in wet conditions. The treatment consisted of intensive tumbling of experimental material assemblies in a specifically designed drum for different periods. The material assemblies were tested before and after simulated wear for waterproofness, and their overall performance was ranked using a newly developed index.

Experimental materials

Six waterproof textile material assemblies containing vapor-permeable membranes used in commercially available protective sailing garments were selected. All six experimental assemblies (Table 1) consisted of three layers: an outer layer, a middle layer and an inner layer (usually described as the lining), laminated together using the method shown in Figure 1(d).
Table 1.
Experimental materials

Sailing garments^a Experimental material assembly

Zhik Isotak Ocean¹⁶ ZIO

Musto HPX Pro¹⁷ MHPX

Zhik Isotak 2¹⁸ ZI2

Musto MPX Race¹⁹ MMPX

Henry Lloyd Offshore Elite²⁰ HLOE

Zhik Aroshell®²¹ ZA

a
Product name as given by manufacturer.

Experimental methods

The physical parameters of all fabrics comprising the experimental material assemblies were determined. The mean mass per unit area of three specimens of each fabric was calculated.²² The thickness of each fabric specimen was measured as the distance between the reference plate and the parallel presser foot of the standard thickness tester,²³ and the mean calculated for each fabric. Mean fabric thread density was determined from the number of warp and weft yarns in 1 cm² of fabric from each of three specimens.²⁴ Mean fabric stitch density was determined from the number of courses and wales of knitted fabrics in 1 cm of three fabric specimens, counted using a pick glass.²⁵

A specifically designed and manufactured wear simulator was used to weather the material assemblies. The simulator consisted of a waterproof drum (420 mm long and 310 mm in diameter) placed on a rotating mechanism to simulate the tumbling, abrasion and impact action experienced by these assemblies during practical wear in wet conditions (Figures 2 and 3).
Figure 2.
Wear simulator.

Figure 3.
Experimental sleeves with enclosed balls inside the drum with water.

The inside of the drum was lined with 240 grit sandpaper (a good representation of the deck grip grit found on boats) and fitted with four aluminum bars. The aluminum bars were used to simulate the edges of marine fixtures and fittings, such as blocks, cleats and tracks. To completely wet the fabrics during the tumbling process without full immersion, 0.500 L of water was added to the drum in each test.

All experimental material assemblies were cut into 13 cm × 30 cm specimens, labeled with the stiffness value of the test ball (7.4 cm in diameter) to be enclosed and the wear testing time to be applied, and stitched into an open sleeve. A ball – A, stiffness 150 kN/m, or B, stiffness 20 kN/m – was then stitched into the sleeve. The balls were of different stiffness to imitate the range of impacts induced by objects during sailing. To determine the stiffness k of the balls, defined as the resistance of an elastic body to deflection or deformation by an applied force (Equation (1)),^26,27 a universal testing machine (Instron 4466) was used and operated at a constant rate of extension with a crosshead speed of 0.5 m/min
$k = dF / dx$
(1)
where k is the stiffness of balls, kN/m; dF is the rate of applied force, kN/min; and dx is the compression rate, m/min.

Six sleeves (one made from each garment) were placed into the drum (Figure 3) and 0.500 L of water added. The drum was sealed and placed on the roller mechanism, which was operated at 60 revolutions per minute for the required duration of mechanical treatment: 30, 60, 90 or 120 minutes. For each duration, a “virgin” set of test sleeve samples was used (i.e. a test sample was not used more than once).

After each wear test, the sleeves were unstitched, dried in an Electrolux TS560 drying cabinet (where warm air circulates at 40℃ for 1 hour), then conditioned at 20℃ and 65% relative humidity (RH) for 24 hours, and finally tested for their resistance to water penetration using a hydrostatic pressure tester under standard ambient conditions.²⁸ In addition, experimental materials were tested in a non-treated state, meaning they did not undergo the wear treatment (results are reported at “0” wear testing time). Readings of hydrostatic pressure were taken at two sites on each unstitched experimental material assembly (Figure 4).
Figure 4.
Test sites of experimental specimens for the hydrostatic pressure test.

An overview of the study design is presented in Figure 5. During hydrostatic pressure testing, each experimental material assembly was subjected to uniformly increased water pressure on its outer side. Hydrostatic head pressure was applied manually, increasing from 0 to 400 kPa at a constant rate of 5 kPa/minute during each test. For the present study, results are reported for the virgin fabric assemblies and the experimental sleeves containing Ball A only (experiments involving the sleeves containing ball B, which created greater impact, will be reported separately).
Figure 5.
Overview of study design.

Three types of behavior were observed during experiments: leaks on the inner side of the sample assembly (Figure 6); assembly rupture without preceding leaks (Figure 7); and no leak or rupture. A leak was defined as an experimental assembly remaining intact but water, under pressure, passing through it and being visible on the other side as droplets. A rupture was defined as an experimental assembly rapidly bursting or tearing. The hydrostatic pressure was recorded at the time of leaks appearing at three different locations (Figure 6) or at the time of rupture (Figure 7); if no fabric rupture or leaks were observed at the maximum applied pressure of 400 kPa, the test was terminated at that pressure. The durability of two fabric performance attributes were separately considered and evaluated: waterproofness and tensile strength.
Figure 6.
Henri Lloyd Offshore Elite material assembly being tested, after 30 minutes of treatment: pressure recorded at appearance of leaks

Figure 7.
Zhik Isotak Ocean material assembly being tested after 120 minutes of treatment: pressure recorded at rupture

In addition to hydrostatic pressure testing, a novel rating scale – the Total Durability Penalty (TDP) index – was developed and used to rate the performance of experimental material assemblies.

Total Durability Penalty index

In order to compare fabrics over multiple performance characteristics, the authors developed a heuristic penalty associated with leaks and ruptures, weighted by the pressure at which they occur, as follows.

The leak penalty term $(K_{l} \frac{{leaks}_{n}}{{pressure}_{l}})$ penalizes the number of leaks ${leaks}_{n}$ , weighted inversely to the pressure at which they first occur ( ${pressure}_{l})$ . Hence, the same number of leaks at a lower pressure will be penalized more than at a higher pressure. K_l is chosen so as to normalize the leak penalty to a range between 1 and 10.

The rupture penalty terms $(K_{rl} \frac{{rupture}_{l}}{{pressure}_{rl}})$ and $(K_{rh} \frac{{rupture}_{h}}{{pressure}_{rh}})$ penalize ruptures at low (≤70 kPa) and high (>70 kPa) pressures, respectively. ${rupture}_{l}$ and ${rupture}_{h}$ are binary variables, taking value 1 when rupture occurs and 0 when it does not. They are again weighted inversely by the respective pressure. $K_{rl}$ and $K_{rh}$ are chosen such that the relative penalty of rupture to leaks is appropriately weighted.

The occurrence of rupture at low pressure is considerably more important than rupture at high pressure, due to the typical conditions of use of these fabrics. Therefore, the penalty for rupture at low pressure should be weighted higher than the penalty for rupture at high pressure. The choice of coefficients is based on numerical convenience, as well as on a subjective assessment of the relative impact of the different kinds of rupture. Multiples of 10 are chosen in order to bring the numerical values of each component of the penalty into the same order of magnitude. Where one penalty should be greater than another, a difference of an order of magnitude provides a sharply differentiated cost. This is sufficient, given that the ordering of weights (more or less expensive) is more important than the specific subjectively chosen ratio. For example, the penalty for a low-pressure rupture should be equivalent to the penalty for 10 leaks; therefore, $K_{rl} = K_{l} \times 10$ . If the high-pressure rupture penalty should be one 10th of the low-pressure rupture penalty, we choose $K_{rh} = K_{rl} 10 = K_{l}$ , which is equivalent to the penalty for one leak.

The TDP index is then given as (Equation (2))
$TDP = K_{l} \frac{{leaks}_{n}}{{pressure}_{l}} + K_{rl} \frac{{rupture}_{l}}{{pressure}_{rl}} + K_{rh} \frac{{rupture}_{h}}{{pressure}_{rh}}$
(2)
where K_l = 10, K_rl = 100, K_rh = 10.

The lower the TDP for each material assembly, the better the overall fabric performance. The minimum theoretical value of the TDP is zero and corresponds to the case with zero ruptures and zero leaks at the maximum pressure, whereas the maximum must be empirically determined.

Statistical analyses

In order to assess the main objective of this study, several statistical analyses were conducted.

A Shapiro–Wilk normality test was carried out to determine the normality of the distribution of the data. The sample values were arrayed by size and the fit against expected means, and variances and covariances were measured. These multiple comparisons against normality give the test more power than other normality tests. The null hypothesis for this test is that the data are normally distributed. P-values, or calculated probabilities, are the probabilities of finding the observed or more extreme results, assuming the truth of the null hypothesis. The significance level, also denoted as alpha or α, is the probability of rejecting the null hypothesis when it is true. If the chosen alpha level is 0.05 and the p-value is less than 0.05, then the null hypothesis that the data are normally distributed is rejected. If the p-value is greater than 0.05, then the null hypothesis is not rejected.

The Kruskal–Wallis H test, a nonparametric test alternative to the one-way analysis of variance (ANOVA) test, was used to identify statistically significant differences between two or more groups of independent variables with respect to a continuous or ordinal dependent variable. The Kruskal–Wallis H test is an omnibus test statistic and cannot determine which specific groups of the independent variables are significantly different from each other; it only determines if at least two groups are different. Since the present study had more than two groups, determining which of these groups differ from each other is important. The Mann–Whitney U-test was used to compare differences between two independent groups when the dependent variable was either ordinal or continuous but not normally distributed.

To determine the strength and direction of an association between two variables measured on at least an ordinal scale, the Spearman rank-order correlation coefficient was used.

The data in the Results section are presented as mean values, and the variability of data around the mean is represented by standard error bars.

Results

The normality test for all experimental fabrics returned a p-value of less than 0.05; therefore, the null hypothesis that the data are normally distributed was rejected. Therefore, the study employed nonparametric data analyses.

Physical parameters

Table 2 summarizes the physical parameters of each fabric in the experimental material assemblies.
Table 2.
Physical parameters of experimental fabrics

Material assembly Components of material assemblies
Mean mass per unit area (g/m²) Mean Thickness (mm) Outer layer
Inner layer

Outer layer: fiber composition^a and construction Middle layer Inner layer: fiber composition and construction Mean warp density per cm Mean weft density per cm Mean thread density per cm² Mean wales (warp) density per cm Mean courses (weft) density per cm Mean stitch (thread) density per cm

ZIO 100% nylon; woven, plain weave Vapor-permeable membrane 100% nylon; warp-knitted, tricot mesh 229 0.49 34 28 62 13 18 31

MHPX 100% polyester; woven, plain weave Vapor-permeable ePTFE membrane 100% nylon: woven, plain weave 285 0.57 26 24 50 66 46 112

ZI2 100% nylon; woven, plain weave Vapor-permeable membrane 100% nylon; warp-knitted, tricot mesh 147 0.33 56 40 96 13 18 31

MMPX 100% polyester; woven, plain weave Vapor-permeable ePTFE membrane 100% nylon; warp-knitted, tricot mesh 200 0.46 34 30 64 14 22 36

HLOE 100% polyester; woven, plain weave Vapor-permeable ePTFE membrane 100% nylon: woven, plain weave 162 0.31 44 40 84 65 43 108

ZA 100% polyester; woven, plain weave Vapor-permeable monolithic membrane 100% nylon; warp-knitted, tricot mesh 174 0.41 70 50 120 13 20 33

^aFiber composition as given by manufacturer label. ZIO: Zhik Isotak Ocean; ZI2: Zhik Isotak 2; ZA: Zhik Aroshell; MHPX: Musto HPX Pro; MMPX: Musto MPX Race; HLOE: Henri Lloyd Offshore Elite; ePTFE: Expanded polytetrafluoroethylene.

Table 2 shows that Musto HPX Pro (MHPX) has the largest mass per unit area and thickness. For the outer layer, Zhik Aroshell (ZA) has the highest warp density, weft density and thread density. For the inner layer, MHPX has the highest wales (warp) density, courses (weft) density and stitch (thread) density.

Pressures of rupture or leaks for different lengths of treatment

A statistically significant difference in pressure (χ²(5) = 21.974, p < 0.001) existed between experimental fabric assemblies that underwent the 30-minute wearing cycle. Events such as rupture or leaks occurred at significantly higher pressure for Zhik Isotak Ocean (ZIO) than all other fabrics (Figure 8). ZIO sustained no leaks or ruptures after 30 minutes of treatment in the wear simulator at a maximum of 400 kPa (Figure 8), and can be categorized as waterproof fabric as per the ratings widely accepted by the industry. Rupture/leak pressures in all paired fabric comparisons, other than Henri Lloyd Offshore Elite (HLOE) and Musto MPX Race (MMPX), were significantly different.
Figure 8.
Hydrostatic head pressure of rupture/leaks for all experimental assemblies after 30 minutes of wear testing. ZIO: Zhik Isotak Ocean; ZI2: Zhik Isotak 2; ZA: Zhik Aroshell; MHPX: Musto HPX Pro; MMPX: Musto MPX Race; HLOE: Henri Lloyd Offshore Elite.

Zhik Isotak 2 (ZI2) ruptured at a mean pressure significantly below the 400 kPa that ZIO resisted, without any leaks, and ZA at a mean pressure 38% lower than ZI2. ZA still passes the minimum requirement for a fabric to be categorized as waterproof because it ruptured at 347.5 kPa, significantly higher (410%) than the accepted minimum of 68 kPa.⁹ The fact that ZI2 ruptures at lower pressure than ZIO is most likely due to the assembly being lighter and thinner (Table 2). However, the hydrostatic head pressure recorded at rupture for this assembly is still high enough for it to be categorized as waterproof. Similarly, ZA probably ruptured at mean pressure 38% lower than ZIO due to being 24% lighter. However, different types of ruptures were observed for ZI2 and ZA: Figures 9(a) and (b) illustrate the ruptures observed in these fabrics at their back side. All three layers in the ZI2 laminate (outer layer, membrane and the inner layer) ruptured. In contrast, the outer layer of ZA did not rupture, only the membrane and the inner layer did (due to the delamination of the membrane from the outer layer, and water pressure building up under the latter).
Figure 9.
Fabric rupture due to applied hydrostatic head pressure (back side of material assembly): (a) rupture of Zhik Isotak 2; (b) Rupture of Zhik Aroshell, with delamination visible as a circle around the breach.

It is clear (Figure 8) that MHPX leaks at significantly lower mean pressure than ZIO (no leaks), ZI2 and ZA, but still passes the minimum hydrostatic head pressure accepted for a waterproof fabric. MMPX and HLOE failed to maintain waterproofness after 30 minutes of wear.

A statistically significant difference in mean pressure existed between experimental fabric assemblies (χ²(5) = 21.942, p < 0.001) that received the 60-minute treatment. As in the 30-minute wear testing cycle, HLOE and MMPX fabric assemblies did not exhibit a statistically significant difference in mean pressure of rupture/leaks, unlike all other paired comparisons.

Figure 10 shows that ZIO maintained its waterproof attributes without any leaks and ruptures despite 60 minutes of wear testing at a maximum of 400 kPa. This is most likely due to the outer layer, membrane and inner layer of ZIO being strongly bonded together. In contrast, for ZI2 and ZA, 60 minutes of wear testing reduced the hydrostatic head pressure value of failure by 27% and 57%, respectively, in comparison to ZIO’s maximum endured pressure of 400 kPa. ZA did not rupture, but leaked after 60 minutes of wear testing at hydrostatic head pressure 30% lower than that after 30 minutes. Comparison of Figures 8 and 10 illustrates that 60 minutes of treatment substantially reduced the hydrostatic head pressures of failure for ZI2 and ZA (by 15% and 30%, respectively) from the 30-minute results. Furthermore, comparison of MHPX after 30 minutes (Figure 8) and 60 minutes (Figure 10) shows that the hydrostatic head pressure of failure was considerably reduced (by 74%). MMPX and HLOE were severely damaged by 60 minutes of wear testing.
Figure 10.
Hydrostatic head pressure of rupture/leaks for all experimental assemblies after 60 minutes of wear testing. ZIO: Zhik Isotak Ocean; ZI2: Zhik Isotak 2; ZA: Zhik Aroshell; MHPX: Musto HPX Pro; MMPX: Musto MPX Race; HLOE: Henri Lloyd Offshore Elite.

Once again, the 90-minute cycle produced statistically significant differences in failure pressure for the experimental fabric assemblies (overall, χ²(5) = 21.554, p = 0.001). The mean failure pressures of ZIO and ZI2 were not significantly different, but each was significantly higher than those of all other fabrics. Failure pressures for HLOE, MHPX and MMPX were not significantly different.

The leaks observed in ZIO after 90 minutes were very small (Figure 11) compared to those in the other experimental fabrics (Figure 6).
Figure 11.
Leaks of Zhik Isotak Ocean after 90 minutes of wear testing.

There were slight decreases in mean failure pressures for ZI2 and ZA after 90 minutes of wear testing compared to those after 60 minutes. After 90 minutes, ZA leaked at a pressure 23% lower than after 60 minutes, indicating greater damage to the membrane. After 90 minutes of wear testing, MHPX, MMPX and HLOE completely failed to maintain the minimum hydrostatic head pressure value to be categorized as waterproof.

The 120-minute wear testing cycle produced a distribution of failure pressures and statistically significant differences (χ²(5) = 21.841, p < 0.001) in the same pattern as the 90-minute cycle (Figure 12). After 120 minutes of wear testing, hydrostatic head pressure values for ZIO and ZI2 were lower by 19% and 13%, respectively, than after 90 minutes (Figure 13).
Figure 12.
Hydrostatic head pressure of rupture/leaks for all experimental assemblies after 120 minutes of wear testing. ZIO: Zhik Isotak Ocean; ZI2: Zhik Isotak 2; ZA: Zhik Aroshell; MHPX: Musto HPX Pro; MMPX: Musto MPX Race; HLOE: Henri Lloyd Offshore Elite.

Figure 13.
Hydrostatic head pressure of rupture/leaks for all experimental assemblies after 90 minutes of applied wear testing. ZIO: Zhik Isotak Ocean; ZI2: Zhik Isotak 2; ZA: Zhik Aroshell; MHPX: Musto HPX Pro; MMPX: Musto MPX Race; HLOE: Henri Lloyd Offshore Elite.

In the case of ZA, no further damage occurred due to the increase in wear testing time from 90 to 120 minutes, but the assembly ruptured instead of leaking. High variation in pressure at rupture was observed among the specimens, as indicated by the error bars in Figure 13.

Figure 14 summarizes the deterioration in durability of all fabric assemblies with increasing length of mechanical treatment: pressure is at an applied maximum of 400 kPa for fabric assemblies at “0” minutes of wear testing (at which none of the assemblies leaked or ruptured) and decreases for all fabric assemblies with increased wear treatment time.
Figure 14.
Hydrostatic head pressure of rupture/leaks for all experimental assemblies at every wear testing time (maximum pressure applied is 400 kPa). ZIO: Zhik Isotak Ocean; ZI2: Zhik Isotak 2; ZA: Zhik Aroshell; MHPX: Musto HPX Pro; MMPX: Musto MPX Race; HLOE: Henri Lloyd Offshore Elite.

Figure 14 demonstrates that the experimental material assemblies ZIO, ZI2 and ZA retain their waterproof rating even after the longest wear testing time, while MHPX maintains technical waterproofness only to 30 minutes of applied treatment and fails thereafter. MMPX and HLOE completely failed after 30 minutes of applied wear and cannot be characterized as waterproof. It is important to note the significant variation in the rates at which the assemblies deteriorate with the application of mechanical treatment, while their performance was identical in the non-treated state.

Relationship between physical parameters of fabrics in material assemblies and rupture and leaks

Statistically significant negative associations exist between rupture of fabric assemblies and the mass per unit area (r_s = −0.622) and thickness of the outer layer (r_s = −0.393). In addition, statistically significant associations exist between rupture and the warp density (r_s = 0.602), weft density (r_s = 0.486) and thread density (r_s = 0.593) of the outer layer of fabric. This means that for the experimental materials, the risk of rupture decreases with increased mass per unit area and the thickness of the outer layer. It also appears that the higher the warp, weft and thread densities of the outer layer, the higher the risk of rupture. This is probably because higher density outer layer fabrics have lower mass per unit area, which could explain the positive relationship between the densities and the risk of rupture. Fabric ZA has the highest density but its mass per unit area is not the lowest; however, only warp density is high, with weft comparable to other fabrics, making the fabric unbalanced in density. Further investigation could consider the influences of the weft and warp densities separately.

Similarly, statistically significant negative associations exist between rupture and the mass per unit area (r_s = −0.622) and thickness (r_s = −0.393) of inner fabrics. In addition, rupture is significantly and negatively associated with the warp density (r_s = −0.524), weft density (r_s = −0.515) and thread density (r_s = −0.515) of inner layer fabrics. Therefore, the higher the mass per unit area and thickness of these fabrics, the lower the risk of rupture.

It was also determined that statistically significant correlations exist between pressure at leakage for both outer and inner fabrics and mass per unit area (r_s = 0.306 for both) and thickness (r_s = 0.306 for both): it appears that the higher the mass per unit area and thickness of these fabrics, the higher the pressure required to cause leaks in the fabric assembly. However, we note that these correlations, as well as the association between rupture and thickness, are quite weak and warrant further investigation.

No statistically significant relationships were found between the pressure at leakage and warp density, weft density or thread density of the outer or inner fabrics.

Total Durability Penalty

The Kruskal–Wallis H test demonstrated that for all wear testing times there were statistically significant differences between TDPs for all experimental fabric assemblies: 30 minutes – χ²(5) = 20.499, p < 0.001; 60 minutes – χ²(5) = 21.961, p < 0.001; 90 minutes – χ²(5) = 21.669, p < 0.001 and 120 minutes – χ²(5) = 21.426, p = < 0.001. In addition, the results of Mann–Whitney U-tests demonstrated that the results for the fabric assemblies within each treatment period were significantly different.

Figures 15(a)–(d) show that the TDPs for HLOE, MMPX and MHPX were significantly higher following all treatment periods than those for ZIO, ZI2 and ZA.
Figure 15.
Total Durability Penalty (TDP) for all material assemblies for 30 minutes (a), 60 minutes (b), 90 minutes (c) and 120 minutes (d) of wear testing. ZIO: Zhik Isotak Ocean; ZI2: Zhik Isotak 2; ZA: Zhik Aroshell; MHPX: Musto HPX Pro; MMPX: Musto MPX Race; HLOE: Henri Lloyd Offshore Elite.

Further, their TDP indices increase with the length of wear testing, indicating increasing damage and loss of waterproof characteristics.

Discussion and conclusions

Standard methods, such as flexing or rubbing tests, are limited in their ability to evaluate the performance of textile materials used in challenging and complex environments, such as sailing. Earlier studies do not fully reflect the complexity of forces and the impact of wet environments on the deterioration of protective sailing apparel. We developed a novel approach to evaluation of the waterproof performance of textile materials, as well as deterioration of tensile strength, by exposing the materials to objects, abrasion and impacts over selected time periods in simulated wear conditions. The TDP index is a useful parameter for ranking the durability of textiles, taking into account both waterproofness and tensile strength, in cases where failures can occur in complex combinations. TDP has potential for use in industrial and commercial product development and evaluation.

Our results show that the rates at which fabric assemblies deteriorate under mechanical wear differ significantly. For example, two fabrics failed to maintain waterproofness after 30 minutes of wear, another failed after 60 minutes, while others maintained water pressure without damage at 200 kPa (∼2000 cm H₂O) after 90 minutes of wear, remaining waterproof according to industry standards.

It appears that mass per unit area and the thickness of the outer and inner fabrics of the assembly influence the pressure at leakage: the higher the mass per unit area and thickness of VPWT fabrics, the higher the pressure at leakage for the assembly. However, no statistically significant relationships were found between pressure at leakage and warp density, weft density and thread density of the outer or inner fabrics. Note that the main aim of the research was to introduce and evaluate the method and the relevant experimental assemblies, rather than to investigate the underlying causes of the materials’ behavior. The latter would warrant a separate extensive study, as the structure of the assemblies and the variables affecting the behavior under wear testing conditions are complex and numerous. For example, we did not characterize the strength of the membranes and the strength of the lamination adhesion, which would certainly influence the results for each assembly. We consider it useful to identify statistically significant correlations, even if they raise more questions than answers; they provide direction for future research with experimental assemblies of a range of values of mass/unit area, densities and thickness, with the strength of the membranes and the adhesion of laminated layers also to be investigated.

It is also important to note that it is clear (see Figure 9) that the durability and strength of the membranes as well as the robustness of the lamination methods used in material assemblies influence the pressure at leakage and pressure at rupture. For example, fabrics ZI2, ZIO are significantly lighter than other tested fabrics, but have significantly higher resistance to leaking and rupture. Further systematic investigation is required to determine statistically significant associations between these factors.

Future research will determine the reasons for the different types of ruptures. Investigations will focus on the mechanical parameters of the materials comprising assemblies, such as their bursting strength, elasticity and tensile strength. It would also be useful to investigate the reasons for the different sizes of leaks and possible links with the density and thickness of materials comprising assemblies, and the types of membrane and their mechanical parameters. This is important, as the membranes used in the ZIO and ZI2 assemblies appeared to have the highest resistance to leaks and ruptures after the mechanical treatments.

In conclusion, the results of this study show that it is important to consider realistic wear conditions and include these in evaluation methods when assessing the long-term performance attributes of protective material assemblies.

Sailing garments^a	Experimental material assembly
Zhik Isotak Ocean¹⁶	ZIO
Musto HPX Pro¹⁷	MHPX
Zhik Isotak 2¹⁸	ZI2
Musto MPX Race¹⁹	MMPX
Henry Lloyd Offshore Elite²⁰	HLOE
Zhik Aroshell®²¹	ZA

Material assembly	Components of material assemblies	Mean mass per unit area (g/m²)	Mean Thickness (mm)	Outer layer	Inner layer
ZIO	100% nylon; woven, plain weave	Vapor-permeable membrane	100% nylon; warp-knitted, tricot mesh	229	0.49	34	28	62	13	18	31
MHPX	100% polyester; woven, plain weave	Vapor-permeable ePTFE membrane	100% nylon: woven, plain weave	285	0.57	26	24	50	66	46	112
ZI2	100% nylon; woven, plain weave	Vapor-permeable membrane	100% nylon; warp-knitted, tricot mesh	147	0.33	56	40	96	13	18	31
MMPX	100% polyester; woven, plain weave	Vapor-permeable ePTFE membrane	100% nylon; warp-knitted, tricot mesh	200	0.46	34	30	64	14	22	36
HLOE	100% polyester; woven, plain weave	Vapor-permeable ePTFE membrane	100% nylon: woven, plain weave	162	0.31	44	40	84	65	43	108
ZA	100% polyester; woven, plain weave	Vapor-permeable monolithic membrane	100% nylon; warp-knitted, tricot mesh	174	0.41	70	50	120	13	20	33

Footnotes

Acknowledgements

We gratefully acknowledge supply of Zhik branded garments by Zhik Pty Ltd for use in this research. All other garments used in this study were purchased through conventional retail channels. All experiments and research activities associated with this study were conducted independently by RMIT University. None of the authors has any association with the manufacturers or products investigated in this research.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship and/or publication of this article.

Supplemental material

Requests for further information on all underlying research materials related to the manuscript, such as data or experimental samples, should be addressed to the corresponding author.

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Material assembly	Components of material assemblies			Mean mass per unit area (g/m²)	Mean Thickness (mm)	Outer layer			Inner layer
Material assembly	Outer layer: fiber composition^a and construction	Middle layer	Inner layer: fiber composition and construction	Mean mass per unit area (g/m²)	Mean Thickness (mm)	Mean warp density per cm	Mean weft density per cm	Mean thread density per cm²	Mean wales (warp) density per cm	Mean courses (weft) density per cm	Mean stitch (thread) density per cm
ZIO	100% nylon; woven, plain weave	Vapor-permeable membrane	100% nylon; warp-knitted, tricot mesh	229	0.49	34	28	62	13	18	31
MHPX	100% polyester; woven, plain weave	Vapor-permeable ePTFE membrane	100% nylon: woven, plain weave	285	0.57	26	24	50	66	46	112
ZI2	100% nylon; woven, plain weave	Vapor-permeable membrane	100% nylon; warp-knitted, tricot mesh	147	0.33	56	40	96	13	18	31
MMPX	100% polyester; woven, plain weave	Vapor-permeable ePTFE membrane	100% nylon; warp-knitted, tricot mesh	200	0.46	34	30	64	14	22	36
HLOE	100% polyester; woven, plain weave	Vapor-permeable ePTFE membrane	100% nylon: woven, plain weave	162	0.31	44	40	84	65	43	108
ZA	100% polyester; woven, plain weave	Vapor-permeable monolithic membrane	100% nylon; warp-knitted, tricot mesh	174	0.41	70	50	120	13	20	33