Sock fabrics: relevance of fiber type,yarn,fabric structure and moisture on cyclic compression

Abstract

The objective of this study was to subject dry and damp sock fabrics to repeated compression cycles in order to determine the relative effects of fiber type (fine wool, mid-micron wool, acrylic), yarn type (high twist, low twist, single) and fabric structure (single jersey, half-terry, terry) on fabric compression and recovery from compression. Changes in fabric thickness were measured using a tensile tester and a number of parameters identified and analyzed: retained thickness, recovered thickness, compression to recovery ratio, energy absorption and energy absorption standardized for fabric thickness. The dominant factor was the number of compression cycles, with most change in the thickness retained and recovered evident within the first 10 cycles. The pattern of response of dry and damp fabrics was quite different with, the dry fabrics having a better compression to recovery ratio. Energy absorption was affected strongly by fabric structure, however this was closely related to initial fabric thickness. When fabrics were made damp, fabrics composed of acrylic fibers had a better compression to recovery ratio than fabrics composed of wool.

Keywords

sock fabrics fiber type fabric structure yarn type cyclic compression thickness moisture content

Protecting tissues of the foot from pain or injury caused by frequent impact is an important function of foot coverings, including socks, thus many types of footwear are designed to absorb shock from walking and running. Foot protection is particularly valuable to people who engage in frequent and extended periods of high impact locomotion (e.g. running, walking, hiking), military activities (long distance road marches carrying heavy loads), or who suffer from soft tissue and joint disorders such as joint degeneration, osteoarthritis, lower back pain, and rheumatoid arthritis.^1,2 Footwear which has been designed to absorb shock may also have a positive effect on the health and comfort of people in occupations where a high percentage of their time is spent standing or walking.³

Socks are increasingly being developed with padding for specialized end uses. For example, high density padding under the metatarsal heads⁴ and/or heel in cushion-soled socks has been claimed to exhibit better shock attenuation properties than a bare foot or wearing a cotton sport sock.⁵

Despite the relative importance of compression and impact absorption properties of socks, understanding has been limited to theoretical modeling of deformation of fibers and yarns independent of fabrics,^6–12 literature on carpets (unpublished), or human wear trials.^5,13,14 The effect of fabric compression on handle and drape has also been investigated.^15,16 The importance of fabric structure on sock compression and capacity to absorb impact has been alluded to;^14,17 however, further work is needed to fully understand how sock fabrics behave under compressive forces.

The relative effects of fiber type, yarn type and fabric structure on the compression and recovery from compression of sock fabrics is not yet known. Much of the focus on compression properties of socks has been on detecting differences between socks of differing fiber types.^5,14 As expected, wool and acrylic cushion-soled socks have both shown a greater shock attenuating effect than walking bare foot.⁵ An increased time to peak force and decreased propulsive force when wearing wool socks compared with bare feet while walking (measured using a force plate) was observed by Blackmore et al.¹⁴ Nevertheless, yarn type and fabric structure also have an effect on sock compression and shock absorption.¹⁷ Terry fabrics absorbed more impact energy (using a ball drop method) than single jersey.¹⁷ Thus, increasing sock thickness is reportedly a means to improve shock attenuating properties; however natural fibers may not possess the resilience needed to attenuate shock.¹⁴ Full details of the sock fabrics used (structure, thickness, yarn type, and mass per unit area) by Blackmore et al.¹⁴ were not provided, thus results may reflect unknown interactions amongst several variables.

There has also been interest in the ability of socks to continue to reduce foot pressure (from repeated contact with the ground) and absorb impact after a period of use. The decrease in the cushioning effect of ‘aged’ socks indicates they may not absorb impact or cushion feet over extended periods of use, with a 31% reduction in the ability of 3 month old socks to reduce foot pressure compared with new socks.⁴ The capacity of a sock to attenuate impact after a high number of footfalls (2068 ± 169) and during high energy impact conditions such as running is uncertain, as differences in actual sock performance have not been detected during running or for runs of long duration (5000 m) as measured using five participants in a laboratory setting.¹⁴ Due to the occlusive nature of footwear and the proclivity of feet to sweat, socks may become damp during use, yet the compressive properties of damp sock fabrics are unknown. Although compressive and energy absorbing properties of socks have been investigated previously, the objective of this study was to subject dry and damp sock fabrics to repeated compression cycles in order to determine the relative effects of fiber type, yarn type and fabric structure on fabric compression and recovery from compression.

Experimental details

Materials and test conditions

A 3 × 3 × 3 × 2 factorial experimental design was used to examine the relative effects of fiber, yarn and fabric structure (Tables 1 and 2) when dry and damp on the compressive properties of sock fabrics. 27 fabrics were manufactured for this work with production variables including knitting machinery (Sangiacomo 4100 HT 12-gauge machine, single cylinder, Christchurch, New Zealand) and tension matched as closely as possible across the different yarn and fiber types. Fabrics were non-dyed.

Table 1.

Fabric variables

Variable	Description
Fiber	Fine wool, 19 µm
	Mid-micron wool, 26 µm
	Acrylic, 19 µm^a
Yarn	Two-fold conventional, R74/2 tex, singles twist factor 2700, two-fold at ∼55%
	Two-fold low twist, R74/2 tex, singles twist factor 2100, two-fold at ∼55%
	Single conventional, R74/1 tex, singles twist factor 2700
Fabric	Terry
structure	Half-terry^b
	Single jersey

Acrylic density was 1.16 g/cm³; 3 denier fiber has a diameter of approximately 19.1 µm.

Half-terry: loops on every second course only.

Table 2.

Properties of sock fabrics (n = 5)

Fiber	Yarn twist	Fabric structure	Stitches per 10 mm (course direction)		Mass/unit area (g/m²)		Thickness (mm)
			Mean	s.d.	Mean	s.d.	Mean	s.d.
Acrylic	High	Single jersey	7.90	0.14	344.80	4.32	1.64	0.05
	Low		7.75	0.25	357.40	9.53	1.69	0.04
	Single		7.50	0.00	340.60	11.76	1.53	0.03
	High	Half-terry	6.70	0.67	449.20	10.71	3.95	0.03
	Low		6.30	0.57	446.50	16.38	4.02	0.03
	Single		6.70	0.45	468.80	13.03	3.91	0.05
	High	Terry	6.60	0.55	515.00	5.66	4.37	0.09
	Low		7.00	0.61	522.80	13.77	4.62	0.07
	Single		6.50	0.71	551.80	6.76	4.28	0.03
Fine-wool	High	Single jersey	8.65	0.22	422.40	5.50	1.61	0.01
	Low		8.65	0.22	437.60	3.21	1.66	0.02
	Single		8.50	0.00	414.60	8.32	1.60	0.03
	High	Half-terry	7.10	0.74	572.20	4.21	3.60	0.07
	Low		6.60	1.52	563.80	16.89	3.66	0.04
	Single		8.05	0.87	568.40	8.96	3.59	0.07
	High	Terry	8.45	0.76	653.60	13.58	4.25	0.04
	Low		8.50	0.50	687.80	19.01	4.40	0.06
	Single		8.50	0.00	678.20	20.13	4.30	0.07
Mid-wool	High	Single jersey	8.50	0.00	402.20	4.66	1.67	0.04
	Low		8.40	0.22	385.40	5.32	1.66	0.04
	Single		8.35	0.22	399.20	4.66	1.65	0.02
	High	Half-terry	6.90	0.55	532.60	9.71	3.73	0.04
	Low		6.70	0.76	498.60	5.32	3.68	0.05
	Single		7.00	0.71	534.80	6.14	3.78	0.05
	High	Terry	7.60	0.42	633.00	8.46	4.53	0.04
	Low		7.60	0.74	607.20	9.55	4.44	0.06
	Single		7.40	0.55	627.80	7.73	4.46	0.04

Fabrics were pre-treated to ensure stability in a Wascator washing machine (FOM71MP-Lab, supplier: James Heal and Co Ltd, Halifax, UK) using six laundering cycles of program 8 A and detergent A, as specified in BS EN ISO 6330:2001, and dried flat after the sixth cycle.¹⁸ Fabrics were conditioned for 24 h prior to testing in the standard environment for conditioning and tested in accordance with EN ISO 139:2005 (i.e. 20.0 ± 2℃, 65.0 ± 4.0% RH).¹⁹ Conditions during testing were recorded using a temperature and RH data logger (Tiny Tag, Gemini Logger Manager (GLM) Tiny Tag. Ultra Energy Engineering, Auckland, New Zealand).

Measurement of cyclic compression on fabric specimens based on well-established techniques for determining cyclic compression, using a tensile testing machine in compressive mode (e.g. Yusof²⁰ and Gore et al.²¹), and is similar to that reported by Morris et al.¹³ An attachment similar to a conventional ball burst but with a flat surface was fabricated for use in the present work (Figure 1). The diameter of the circular surface at the bottom of the attachment was 35.7 mm, giving a fabric contact area of 1000 mm². The compressive attachment was mounted in the upper jaw of an Instron tensile tester (Model 4464, supplier: BioLab Limited, Auckland, New Zealand). The sock fabric specimen (70 × 70 mm, n = 5) was attached to a steel platen (70 × 70 mm) mounted in the lower jaw, technical rear side up using a single piece of double-sided adhesive (70 × 70 mm) applied to the technical face of the specimen. A 100 N load cell ± 0.5% reading accuracy was used. The tensile tester was programmed to cycle between 0 and −30 N (giving a compressive pressure of 30 kPa over the contact area of the specimen) for 50 cycles with a crosshead speed of 10 mm/min. The standing peak pressure range under feet of adult humans ranges from 8.7–138.9 kPa, varying considerably in the different plantar regions of the foot;²² therefore 30 kPa was selected as a representation of foot pressure within this range. Data were collected as force by time at a sampling rate of 100 points per second using a Powerlab (supplier: ADInstruments, Dunedin, New Zealand) and were recorded using LabChart® software.²³

Figure 1.

Compression instrument set-up.

The test sequence was repeated using damp fabric specimens. Prior to being adhered to the platform, specimens were made damp using a wetting cycle (2 kg load, 20℃, rinse gentle action (180 s), drain no action (60 s), extract slow (30 s), drain gentle action (30 s)) in a Wascator washing machine as previously reported by Laing et al.²⁴ Specimens were then placed immediately into re-sealable plastic bags and kept in the standard environment prior to use. Specimens remained in the bags for no more than 8 h. No effort was made to standardize the volume of water held in the specimens, as the treatment was intended to reflect actual use where the fabrics would absorb what they would (e.g. rain, immersion, sweating foot). Damp and dry specimens were tested in a fully randomized order.

Analysis

Data were pre-processed using a set of macros written in Microsoft Visual Basic® in Excel® then analyzed using SPSS®.^25,26 The data baseline for each file was determined using the first 100 points. Noise was reduced using an Excel de-spike macro (any noise spikes outside the normal bandwidth range were removed using averaged adjacent points), then the sign of the force values inverted for ease of processing. The maximum force for each cycle was calculated by averaging three points at maximum. Due to the differing shapes of the curves after the unloading cycle, the zero force was found by progressively fitting a 49 point (0.5 s) regression line to the curve (13 specimens needed a 199 point (2 s) regression line in order to accurately determine the minimum). The point in time where the regression line slope equaled zero was taken as the zero force.

Data collected as time in seconds were converted into mm using test speed to determine changes in fabric thickness. All fabrics differed in initial thicknesses therefore comparing changes in absolute thickness was inappropriate. Instead, the thickness a fabric retained under the compressive force or recovered after unloading was converted to a percentage of its initial thickness. Retained and recovered fabric thicknesses are expressed as a percent of the mean initial fabric thickness (see Table 2). The retained fabric thickness at maximum compression and recovered thickness at the end of the unloading phase of each cycle were analyzed both as separate parameters and also as a ratio referred to as the compressive ratio (CR):

CR = \frac{Retained thickness}{Recovered thickness}

Energy absorbed (Joules) by the fabric during compression was calculated from the area under the curve for each cycle using Simpson’s rule to determine the work (Figure 2). The amount of energy absorbed was influenced largely by initial fabric thickness; therefore, energy absorbed was standardized for fabric thickness in order to better determine the relative effects of fiber type, yarn type and fabric structure by dividing the area by mean initial fabric thickness:

Energytothickness = \frac{Energy}{Fabricthickness}

A mixed model analysis of variance was used to explore the effects of: number of compression cycles; fiber, yarn, fabric structure and moisture content for retained thickness; recovered thickness; compression to recovery ratio; energy absorbed and energy absorbed standardized for fabric thickness. A first order auto-regressive correlation model (IBM® SPSS® AR1) was used within the ANOVA for the cycle factor. Specimens were analyzed in two ways. The first analysis, referred to as “all cycles”, compared every cycle with every other cycle (excluding 1, 47, 48, 49 and 50: cycles 47, 48, 49, and 50 were excluded to create 5 groups of 9 cycles; cycle 1 was excluded as data from the beginning of the cycle could not be compared with a previous cycle as this was the start of the test). Only selected second and third order interactions could be included in the first analysis as there were convergence problems in SPSS® due the mixed model limit on the number of parameters fitted (inclusion of too many parameters caused the model to fail). In many cases (e.g. the recovery phase of the cycling) only the main effects could be analyzed, thus analysis of interactions was excluded. Secondly, cycles in five aggregated blocks (2–10, 11–19, 20–28, 29–37, 38–46) were examined in order to compare means among groups at the beginning of the test and at the end of the test. This analysis is referred to as “aggregated cycles”. All second and third order interactions were included in this analysis as there were no convergence problems within SPSS®. Thus, effects of all interactions could be reviewed. The Sidak comparison was used as a post hoc procedure to determine which means differed among the factor levels.²⁷ First and second order interactions were explored and discussed in depth only where results were both significant and the corresponding F values were large.

Figure 2.

Compression analysis parameters (inverted data). a: Maximum; b: minimum; c: area; d: initial thickness; d_r: thickness retained; d_c: recovered; x: thickness compressed up to 30 N; y: thickness recovered up to 0 N.

Results and discussion

All compression properties of the sock fabrics decreased significantly with an increasing number of repeated compression cycles, regardless of moisture content, fabric structure, yarn type or fiber type.

Number of compression cycles

The largest effect on changes in compression behavior of sock fabrics was attributable to the number of compression cycles. Sock fabrics consistently exhibited the most change in thickness retained, recovered the greatest thickness and absorbed the most energy during the early compression cycles (e.g. 2–10). These changes in thickness were likely due to the deformation/re-arrangement of the fibers and/or yarns, previously observed in pile fabrics as buckling of the pile, bending, and finally compression of the bent pile into the fabric.²⁸ Processes involving deformation of fibers and yarns have been observed in other cyclic testing, and as observed in the current work most change occurred during the initial stages.^18,20,29 For example, when a fabric is laundered multiple times, most dimensional change occurs during the first three laundering cycles¹⁸ generally in the form of relaxation shrinkage due to re-arrangement of the loops/yarns.³⁰ Cyclic experiments examining stiffness of cervine leather have also identified the number of cycles to be an important factor, with the largest change in stiffness between cycles 1 and 4.²¹ Although the current work only examined socks up to 50 compression cycles, it seems plausible that the number of cycles would continue to be a dominant factor if more cycles were examined. For example Blackmore et al. reported a specialist running sock had better shock attenuating effects before a run, but differences were not detected among the specialist running sock, a non-specialist running sock and bare feet after the run (5000 m), possibly due to the high number of footfalls (2068 ± 169).¹⁴

Moisture content

Moisture significantly affected the compressive behavior of fabrics with damp fabrics not absorbing as much energy (when standardized for fabric thickness), nor retaining or recovering as much thickness as dry fabrics. These differences appeared to be due mainly to fiber hygroscopicity, and to a lesser extent fabric structure. In terms of fiber, both wool fabrics absorbed much higher percentages of water than the acrylic fabrics, which may have contributed to their lesser thickness retention and recovery relative to the acrylic (Table 3). Natural fibers have a greater affinity for water, thus making them more easily compressed.^31,32 This may be linked to the bending modulus of the fiber, as wool fibers have a lower bending modulus than acrylic when dry.³³ The bending modulus of wool further decreases with increased humidity,³⁴ although the bending modulus of some synthetic fibers also responds to increases in relative humidity (e.g. nylon 6.6).^34,35 Whether this applies to acrylic fiber is not known, as a published value for the bending modulus of acrylic with changing RH could not be located.

Table 3.

Percentage of water absorbed, expressed as a percentage of dry fabric weight, and percentage of mean thickness retained of damp fabrics following compression

			Water absorbed		Mean percentage thickness retained
Fiber	Yarn	Structure	Percentage	s.d.	2–10 cycles	11–19 cycles	20–28 cycles	29–37 cycles	38–46 cycles
Acrylic	Single	Jersey	42.4	3.1	33.41	30.00	28.40	27.48	26.86
Acrylic	High	Jersey	43.1	3.6	36.93	34.41	32.03	29.93	28.67
Acrylic	Single	Half-terry	43.6	4.3	45.23	41.46	39.75	38.23	37.23
Acrylic	Low	Jersey	47.2	5.9	32.45	29.37	27.98	27.12	26.63
Acrylic	Low	Half-terry	47.6	3.7	36.13	32.75	31.35	30.39	29.71
Acrylic	High	Half-terry	48.7	2.0	38.20	34.76	33.24	32.24	31.45
Acrylic	Low	Terry	49.0	3.1	39.17	35.54	33.90	32.72	31.76
Acrylic	Single	Terry	49.7	4.7	43.78	39.36	37.58	36.38	35.49
Acrylic	High	Terry	51.3	2.2	40.24	36.00	34.22	33.05	32.27
Mid-micron wool	Single	Terry	67.8	4.5	41.96	35.84	33.58	32.30	31.14
Mid-micron wool	High	Half-terry	68.0	3.5	42.83	37.44	35.26	33.95	33.11
Mid-micron wool	Low	Terry	68.6	5.8	39.42	33.65	31.44	30.10	29.18
Mid-micron wool	Low	Half-terry	69.7	10.3	45.13	40.05	38.15	36.80	35.78
Mid-micron wool	Low	Jersey	71.4	3.7	32.33	28.62	27.26	26.56	25.93
Mid-micron wool	Single	Half-terry	72.2	4.5	47.18	41.20	38.65	37.14	36.26
Mid-micron wool	High	Jersey	72.3	12.7	32.10	28.04	26.57	25.72	25.01
Fine wool	Low	Jersey	73.1	1.7	29.24	25.92	24.78	24.02	23.40
Fine wool	Single	Jersey	74.7	2.3	28.70	25.35	24.25	23.53	22.98
Fine wool	High	Jersey	75.3	6.4	31.33	27.67	26.49	25.59	24.93
Mid-micron wool	Single	Jersey	77.4	8.1	32.24	28.68	27.24	26.43	25.76
Mid-micron wool	High	Terry	77.8	8.8	39.41	34.48	32.64	31.23	30.23
Fine wool	High	Half-terry	78.4	3.3	44.46	38.25	35.57	33.89	32.54
Fine wool	High	Terry	80.4	4.4	38.99	33.96	31.96	30.56	29.51
Fine wool	Low	Half-terry	83.6	11.6	42.39	36.34	33.92	32.31	31.18
Fine wool	Single	Half-terry	85.7	0.7	45.97	39.20	36.46	34.76	33.62
Fine wool	Single	Terry	88.2	7.9	42.93	37.17	34.93	33.52	32.38
Fine wool	Low	Terry	88.3	4.2	38.69	33.40	31.14	29.64	28.62

Fiber type

Fiber had the least effect on the compressive properties of sock fabrics. The property it most significantly affected was the compression to recovery ratio, with acrylic fabrics recovering better and retaining slightly more thickness than mid wool and fine wool fabrics (Figure 3). Acrylic socks have previously been reported as retaining thickness better than wool socks due to wool fibers absorbing water and thus compressing more easily than acrylic fibers.³¹ The smaller amount of water present within the acrylic fabrics allowed the damp acrylic fabrics to exhibit a pattern of response that closely resembled that of dry fabrics (Figure 4(a)). This is probably due to the acrylic fabrics containing less water than both types of wool fabrics, as mentioned previously. The current work suggests that hygroscopicity may be the most important contribution of fiber type on compressive properties of fabrics.

Figure 3.

Thickness retained (%) of fabrics under compression by cycle. (a) Dry acrylic fabrics; (b) damp acrylic fabrics; (c) dry fine wool fabrics; (d) damp fine wool fabrics; (e) dry mid-micron wool fabrics; (f) damp mid-micron wool fabrics.

Figure 4.

Compression to recovery thickness ratio. (a) Fiber and moisture content. (b) Structure and moisture content.

Fabric structure

After the number of cycles, fabric structure had the greatest effect on the amount of energy absorbed. However, the differing amounts of energy absorbed appeared to be directly related to the differing initial fabric thicknesses, with jersey being thinnest and absorbing the least, followed by half-terry and then terry which absorbed the most energy and was also thickest. When the energy absorbed was standardized for fabric thickness, fabric structure did not have a significant effect (Table 4). Therefore, the difference in the compressive behavior of the three fabrics appears to be mostly related to initial fabric thickness rather than to inherent structural differences. Fabric thickness has previously been linked to energy absorption by Baussan et al., who found the thickest terry fabric had the best shock absorbing effect (energy absorption),¹⁷ and Blackmore et al., who reported a high correlation coefficient between sock thickness and peak impact force,³⁶ time to peak impact force and loading rate over 10 repeated impacts for socks (without shoes). Therefore, it is not surprising that increasing fabric thickness has been suggested as a method to improve shock absorbing properties of socks,^5,14 and as the current work demonstrates, fabric thickness is largely influenced by fabric structure.

Table 4.

Principal factors affecting compression parameters (all cycles)

Parameters and variables	df	F	Sig.
Percent of original fabric thickness
Cycle	44	81.55	0.001
Fiber	2	0.14	NS
Yarn	2	17.70	0.001
Fabric structure	2	146.02	0.001
Moisture content	1	432.02	0.001
Cycle × structure	88	2.91	0.001
Cycle × moisture content	44	10.53	0.001
Structure × moisture content	2	0.13	NS
Percent of original fabric thickness recovered
Cycle	44	59.78	0.001
Fiber	2	0.70	NS
Yarn	2	22.01	0.001
Fabric structure	2	176.10	0.001
Moisture content	1	686.03	0.001
Cycle × structure	88	1.22	NS
Cycle × moisture content	44	7.49	0.001
Structure × moisture content	2	0.06	NS
Fiber × yarn	4	3.60	0.01
Compression to recovery thickness ratio
Cycle	44	21.76	0.001
Fiber	2	36.68	0.001
Yarn	2	3.54	0.05
Fabric structure	2	84.59	0.001
Moisture content	1	600.18	0.001
Structure × moisture content	2	22.33	0.001
Fiber × structure	4	8.68	0.001
Fiber × moisture content	2	132.57	0.001
Energy absorbed
Cycle	44	137.12	0.001
Fiber	2	2.33	NS
Yarn	2	2.03	NS
Fabric structure	2	433.95	0.001
Moisture content	1	118.48	0.001
Cycle × structure	88	14.13	0.001
Cycle × moisture content	44	13.29	0.001
Structure × moisture content	2	14.13	0.001
Energy absorbed standardized for fabric thickness
Cycle	44	63.47	0.001
Fiber	2	1.24	NS
Yarn	2	0.44	NS
Fabric structure	2	0.29	NS
Moisture content	1	56.93	0.001
Cycle × fiber	88	0.84	NS
Cycle × moisture content	44	5.90	0.001
Fiber × moisture content	2	2.90	NS

Differences in behavior of the fabric structure, possibly related to fabric density, were more apparent when the compression to recovery ratio was examined. Single jersey had a much lower ratio than terry and half-terry, presumably due to the terry loop structure (which creates a less dense structure than single jersey). Increased fabric thickness and density have been indicated as possible contributors to improve shock attenuating properties of socks by Howarth and Rome;⁵ however the authors did not report these parameters. Fabric density is reported to improve shock attenuation by providing a framework of material to dissipate shearing forces, possibly enhancing the properties of the fibers, particularly acrylic.⁵ Thus, the current work suggests that the inherent properties of different fabric structures (e.g. density and thickness) are possibly more important than the geometric arrangement of yarns within the fabric structure for repeated compressions of up to 50 cycles.

Yarn structure

Yarn structure appears to have little effect on the compression properties of sock fabrics. The small differences that were detected among fabrics constructed from differing yarns indicated that fabrics composed of single ply yarn retained a higher percentage of their original thickness during compression and recovery than fabrics composed of plied yarns. This is possibly related to fabric density, as fabrics composed of single yarns were thinner but had a higher mass per unit area than fabrics composed of plied yarns. Any appreciable influence that yarn type has on the compressive properties of sock fabrics appears to be linked to the yarn role in shaping the fabric structure, and thus the influence of this on thickness and density, both of which have been identified by Howarth and Rome as influencing compressive properties.⁵

Conclusions

The carefully controlled manufacture of sock fabrics allowed the relative effects of sock components on compression properties to be analyzed. Although the number of compression cycles in the current work (50) was much lower than that to which a typical sock would be subjected during wear, this was sufficient to identify relative differences in patterns of response to cyclic loading (after stabilization, with most changes in thickness occurring within the first 10 cycles). The most important factor was whether the fabrics were dry or damp, as damp fabrics absorbed less energy, retained less thickness during compression and recovered less than dry fabrics, much of which was influenced by fiber hygroscopicity. Fabric structure was less important, as the compressive properties of a fabric were influenced mostly by initial thickness, and to a lesser extent, fabric density, both of which are inherently controlled by the fabric structure. When energy absorbed was standardized relative to initial thickness, only the number of cycles and whether a fabric was dry or damp were significant factors. Since most of the parameters investigated can be managed by the sock manufacturer or specified by those involved in the design of socks, clarification of the relative effects of fiber, yarn and fabric structure on compressive behavior of socks is useful in order to produce socks with desirable characteristics.

Footnotes

Acknowledgments

Dr Stewart Collie of AgResearch is gratefully acknowledged for providing experimental fabrics. The Todhunter/Carpenter/Home Science Alumnae Scholarship fund, the University of Otago Christchurch Earthquake Extension fund, and the University of Otago Department of Applied Sciences are acknowledged for providing tuition fees and/or living stipend.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

References

Light

McLellan

Klenerman

. Skeletal transients on heel strike in normal walking with different footwear. J Biomech 1980; 13(6): 477–480.

Veves

Hay

Boulton

AJM

. The use of specially padded hosiery in the painful rheumatoid foot. The Foot 1992; 1(4): 175–177.

Chiu

M-C

Wang

M-JJ

. Professional footwear evaluation for clinical nurses. Appl Ergonom 2007; 38(2): 133–141.

Veves

Masson

Fernando

DJS

. Studies of experimental hosiery in diabetic neuropathic patients with high foot pressures. Diabetic Med 1990; 7(4): 324–326.

Howarth

Rome

. A short-term study of shock-attenuation in different sock types. The Foot 1996; 6(1): 5–9.

Carnaby

Pan

. Theory of the compression hysteresis of fibrous assemblies. Text Res J 1989; 59(5): 275–284.

Komori

Itoh

. A new approach to the theory of the compression of fiber assemblies. Text Res J 1991; 61(7): 420–428.

Neckář

. Compression and packing density of fibrous assemblies. Text Res J 1997; 67(2): 123–130.

Bogaty

Hollies

NRS

Hintermaier

Harris

. The nature of a fabric surface: Thickness–pressure relationships. Text Res J 1953; 23(2): 108–114.

10.

Dunlop

Jie

. The dynamic mechanical response of carpets. J Text Inst 1989; 80(4): 569–578.

11.

Dayiary

Shaikhzadeh Najar

. A new theoretical approach to cut-pile carpet technology based on elastic-stored bending energy. J Text Inst 2009; 100(8): 688–694.

12.

Van Wyk

. 20—Note on the compressibility of wool. J Text Inst Trans 1946; 37(12): T285–T292.

13.

Morris

Prato

White

. Relationship of fiber content and fabric properties to comfort of socks. Clothing Text Res J 1984; 3(1): 14–19.

14.

Blackmore

Ball

Scurr

. The effect of socks on vertical and anteroposterior ground reaction forces in walking and running. The Foot 2011; 21(1): 1–5.

15.

Choi

Ashdown

. Effect of changes in knit structure and density on the mechanical and hand properties of weft-knitted fabrics for outerwear. Text Res J 2000; 70(12): 1033–1045.

16.

Dupuis

Popov

Viallier

. Compression of greystate fabrics as a function of yarn structure. Text Res J 1995; 65(6): 309–316.

17.

Baussan

Bueno

Rossi

. Analysis of current running sock structures with regard to blister prevention. Text Res J 2013; 83(8): 836–848.

18.

Gore

Laing

Wilson

. Standardizing a pre-treatment cleaning procedure and effects of application on apparel fabrics. Text Res J 2006; 76(6): 455–464.

19.

International Organization for Standardization, ISO 139:2005 Textiles. Standard atmosphere for conditioning and testing. Geneva, International Orgnization for Standardization, 2005.

20.

Yusof NA. Effect of seam type on selected seam tensile behaviour under multi-axial forces. PhD Thesis, University of Otago, Dunedin, New Zealand, 2012.

21.

Gore

Laing

Carr

. Extension and recovery of cervine garment leather. J Soc Leather Technol Chem 2004; 88(2): 56–62.

22.

Cavanagh

Rodgers

Iiboshi

. Pressure distribution under symptom-free feet during barefoot standing. Foot and Ankle 1987; 7(5): 262–276.

23.

ADInstruments. Labchart® 7 Pro (Version 7.2.1), Dunedin, New Zealand, 2011.

24.

Laing

Wilson

Gore

. Determining the drying time of apparel fabrics. Text Res J 2007; 77(8): 583–590.

25.

Microsoft Corporation. Microsoft Visual Basic® 6.5 (Version 1054), Redmond, Washington, 2006.

26.

IBM Corporation. IBM® SPSS® Statistics (Version 21.0.0.0), Chicago, IL, USA, 2012.

27.

Abdi

. The Bonferroni and Šidák corrections for multiple comparisons. Encyclopedia of Measurement and Statistics, Thousand Oaks, CA: Sage Publications, 2007, pp. 103–107.

28.

Finch

. Compressional behavior of textile materials. I. Measurement at a constant rate of deformation. Text Res J 1948; 18(3): 165–177.

29.

Webster

Laing

. Effects of repeated extension and recovery on selected physical properties of ISO-301 stitched seams. Part 1: Load at maximum extension and at break. Text Res J 1998; 68(11): 854–864.

30.

Postle

. Dimensional stability of plain-knitted fabrics. J Text Inst 1968; 59(2): 65–77.

31.

Euler

. Creating “comfort” socks for the U.S. consumer. Knitting Times May 1985, pp. 47–50.

32.

Herring

Richie

. Friction blisters and sock fiber composition: A double-blind study. J Am Pod Assoc 1990; 80(2): 63–71.

33.

Owen

. The application of Searle's single and double pendulum methods to single fibre rigidity measurements. J Text Inst Trans 1965; 56(6): T329–T339.

34.

Chapman

. The bending stress-strain properties of single fibres and the effect of temperature and relative humidity. J Text Inst 1973; 64(6): 312–327.

35.

Hearle

JWS

Miraftab

. The flex fatigue of polyamide and polyester fibres. J Mat Sci 1991; 26(11): 2861–2867.

36.

Blackmore

Jessop

Bruce-Low

. The cushioning properties of athletic socks: An impact testing perspective. Clin Biomech 2013; 28(7): 825–830.