Effects of two different battings (sheep wool versus polyester microfiber) in an outdoor jacket on the heat and moisture management and comfort sensation in the cold

Subjects

Twelve healthy well-trained male sport students of the Department of Sport Science of the University of Innsbruck (Austria) volunteered to participate in this study (age: 23.7 ± 1.7 years; mass: 76.1 ± 3.8 kg; height: 184 ± 5 cm BMI: 22.7 ± 1.2; physical activity: 10.2 ± 4.5 h/w). Participants provided written informed consent, and the study was approved by the Institutional Review Board and the Ethical Commission of the University of Innsbruck.

Physical activity of 10 hours per week demonstrates that participants were not untrained and performed regular sports. In a recent study, maximum relative oxygen consumption (VO₂max) of 67.3 ml/min/kg of male sport students (Department of Sport Science, Innsbruck) was measured during maximal spiroergometry. ¹² Calculated for leg cycling, measured VO₂max would conform to a maximum power of approximately 384 W (J/s). ¹³

Study design and climatic condition

Each subject performed the test protocol (see below) two times with a two-layer outdoor clothing system consisting of a long-sleeve shirt and a jacket. The batting of the jacket was either sheep wool (TW) or PMF (Table 1). Jackets were randomly distributed between the participants. Participants wore the same long-sleeve shirt, soft shell pants, socks, gloves, and cap during all tests and were advised not to change their eating habits and not to perform strenuous activities one day before testing. The resting time between the two tests was at least two days. It was considered that both tests were executed at the same time during the day (e.g. if a person executed the first test in the morning, the second test was also executed in the morning). The investigation was performed in the climatic chamber (Kältepol, Austria) of the Centre of Technology of Ski and Alpine Sport at the Department of Sport Science (Innsbruck, Austria). The climatic condition was set at −5℃ and 40% RH. A temperature of −5℃ was chosen because it reflects a common temperature in winter in Tirol (Austria) on the mountains. For instance, −5℃ is a daily mean (years 1971–2000) in January and February in Obergurgl at an altitude of 1938 m. ¹⁴ A low RH was chosen to guarantee evaporation through the outdoor apparel.

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Table 1.

Characteristics of the jackets filled with tirolwool (TW) and polyester microfiber (PMF) and of the remaining outdoor clothing components. Values of properties are presented as Mean ± SD

	Test jackets						Remaining clothing components
	TW			PMF			Long- sleeve shirt	Soft shell pants		Socks	Gloves	Cap
Construction, fibers (%)	Outer layer	Padding	Inner layer	Outer layer	Padding	Inner layer		Outer material	Mesh inner lining
Construction	Plain weave	non- woven	Plain weave	Plain weave	non- woven	Plain weave
Elastane							3	6		15	9	13
Merino wool							80	20	52	60
Nylon										5
Polyamide	100		100	100		100	17	74			38
Polyester									48	20	53	87
Polyester micro fiber					100
Polylactides		12
Sheep wool (tirolwool)		88
Properties		TW			PMF		Long- sleeve shirt	Soft shell pants		Socks	Gloves	Cap
Air permeability (mm/s)	50.10 ± 3.54			32.57 ± 7.09
Rct (m2K/W)	0.190 ± 0.085			0.202 ± 0.016
Ret (m2Pa/W)	8.88 ± 3.73			10.81 ± 1.27
Thickness – whole jacket (mm)	4.24 ± 1.24			2.80 ± 0.56
Thickness – lower back (mm)	4.080 ± 0.439			3.921 ± 0.438
GSM (g/m2)	305.43			303.04
Weight (g)	654 ± 16			604 ± 9			198 ± 4	488 ± 11		86 ± 2	46 ± 1	34

According to the manufacturer of the climatic chamber, temperature and humidity can be kept in the range of ±1℃ (from 60 to −30℃) and ±3% (from 60 to −5℃), respectively. RH at temperatures below −5℃ cannot be regulated constantly due to the low saturated vapor pressure of the environment. For checking purposes, RH and temperature were recorded during the measurements. RH and temperature could be kept at 43.5 ± 1.6% and −4.7 ± 0.3℃ and at 43.1 ± 1.6% and −4.5 ± 0.3℃ with TW and PMF, respectively. Environmental temperature and RH did not differ significantly between the two test conditions.

Outdoor apparel

The test jackets were constructed with the same inner and outer layer and differed only with respect to their batting. Jackets filled with TW and PMF had the same fit, cut, and construction and were manufactured by the same producer. Variation of body mass and height of test persons were low and therefore just one person wore a smaller jacket (M) than the others (L). The difference in weight between the two sizes (M and L) was 52 g for TW and 32 g for PMF.

Material tests with jackets in size M were conducted at the Institute for Textile Chemistry and Textile Physics in Dornbirn (Austria) regarding the construction, air permeability, thermal resistance (Rct), water vapor resistance (Ret), thickness, and gram per square mass (GSM) of the jackets (Table 1).^15,16 The PMF batting was a non-woven made up of staple fibers with a length of 40–60 mm. Some material properties fluctuated during the measurements demonstrated by their high standard deviations (Table 1). Material tests revealed that both jackets had a high stitch concentration and in a non-uniform pattern, resulting in a fluctuating thickness. Furthermore, the variation in stitch density and thickness affects material properties causing a relatively high standard deviation throughout the material testing. The PMF batting partly showed a higher lofting between the stitching, which had a great influence on the result of the thickness measurement of the whole jacket. The pressure used to measure the thickness was a standard value of 980 Pa (100 g/10 cm²) and it had a much greater effect on the PMF batting than on the TW batting. Comparing the thickness result of our first measurement of the whole jacket with the result of our second control measurement of the lower back demonstrates this problem. The thickness of PMF differed massively between the two tests. Due to the pressure applied, the thickness measurements are actually artificial and not that relevant for insulating materials that are soft. As the jackets were not flat, the thickness measurements without an additional force would have been unreliable. This is a common problem and some people have been coming up with new methods, but none of them have been standardized yet.

To sum up, results indicate that air permeability of TW must have been higher and Ret lower compared to PMF, but it cannot be stated that Rct differed significantly between the jackets.

Test protocol

The test protocol had two phases: participants walked on a treadmill (pulsar, h/p/cosmos, Germany) with 7.7% inclination and a walking speed of 5 km/h (walking period) for 1 hour. The altitude covered was 375 m. After the physical activity, participants rested in an upright position leaning at a table for 20 minutes (cool-down period). Testing cold weather apparel often requires exposure times of an hour or longer to evaluate physiological responses sufficiently and to stabilize and reach a steady state. ¹⁷ The executed test protocol lasted overall 86 minutes with additional four 1.5 minute measuring intervals. The activity corresponded to a relative oxygen uptake (VO₂rel) of 27 ml/min/kg, an uptake that will be approximately 40% of the maximum oxygen uptake (VO₂max) of sport students who were tested at the Department of Sport Science in Innsbruck in May 2012.^12,18 A test person with a body height of 1.84 m and weight of 76.1 kg had theoretically a metabolic energy production (M) of approximately 366 W/m² (if respiratory quotient was 1) during walking. ¹⁷ The test protocol should reflect a common activity (e.g. hiking, ski touring with light intensity) with a subsequent cooling phase in wintertime in the mountains.

Measurements

Parameters representing the heat and moisture management were core temperature, skin temperature, absolute humidity underneath the shirt and jacket, surface temperature of the jacket, sweat production, evaporation, and sweat residues. The subjective comfort enfolded the thermal sensation and the sensation of scratching. Perceived exertion, sensation of pain, register of shivering, and heart rate were additionally elicited. Core temperature, surface temperature, and subjective sensations were determined every 20 minutes. Humidity, skin temperature, and heart rate were continuously recorded.

The core temperature was measured in the right ear canal by IR-Tympanometry (ThermoScan IRT 4520, Braun, Germany). ¹ Before every usage the measuring device was stored in the antechamber and carried in the jacket of the investigator to prevent malfunction during measurement in the cold. Core temperature was determined without movement of the test persons (within a 1.5 minute interval) after every 20 minutes. Thermal sensors (platinum thermal sensor M222, Heraeus, Germany) were attached on the chest (pectoralis), upper back (scapula), and upper arm (deltoid and triceps) for measuring the skin temperature of the upper trunk. Additional sensors (SHT 15, Sensirion, Switzerland) were attached underneath the shirt (right pectoralis, left scapula) and jacket (left pectoralis, right scapula) for calculating absolute humidity within the clothing system. Temperature and humidity data were recorded with data loggers and analyzed with MatLab Ver. R2012a (USA). For the statistical analysis, the data were averaged over the last five minutes of 20-minute intervals. Thermography images (VarioCam high resolution, Infratec, Germany) were captured without movement of the front and back of the jacket for determining the outer surface temperature.

Participants were weighted (DS150K1, Kern, Germany) in underpants and completely dressed at the beginning and at the end of the investigation for calculating sweat production and evaporation. The quotient of evaporation and sweat production represented the relative evaporation. Jacket, shirt, and pants were weighted separately at the start and end of the tests for calculation of the sweat residues.

Thermal and tactile comfort questions were related to the upper body. The thermal sensation was assessed with a nine-point thermal rating scale (from 4 very hot to −4 very cold, modified from ISO-10551, 1995) and the tactile sensation “scratching” with a seven-point scale (from 7 no sensation to 1 totally felt).^5,17 In addition, it was observed if the participants shivered. Perceived exertion was evaluated with the Borg scale (6–20, from no exertion at all to maximal exertion) and perceived pain with a five-point scale (from 0 none to 5 severe).^17,19 At the end of the test protocol, participants made a subsequent assessment if they felt their thermal status acceptable during the whole protocol. ¹⁷ Heart rate (wear link + transmitter w.i.n.d, Polar, Finland) was recorded with the treadmill software (para graphics, h/p/cosmos, Germany) and calculated exactly as well as the skin temperatures and microclimates for the statistical analysis.

Statistics

Analysis of variance (ANOVA) with repeated measurement (factor 1: batting, factor 2: time) was used to determine parameter differences between TW and PMF for the walking (start to 63 minutes) and cool-down period (from 63 to 84.5 minutes). With the same statistical method, core temperature was additionally analyzed over the whole test protocol (walking + cool - down). Weight parameters were analyzed with t-tests for matched pairs. If parameters were not normal distributed, the Wilcoxon and McNemar tests were applied. In addition, correlation analysis between the progress of moisture underneath the shirt and comfort sensations were executed with Pearson’s correlation. Values are reported as mean values ± standard deviation (Mean ± SD). Differences and correlations were considered as statistically significant at p ≤ 0.05. Parameters were analyzed with the program SPSS Statistics Ver. 18 (IBM, USA).

Core and skin temperature

From the start to the end of the whole test protocol (from minute 0 to 84.5) core temperature dropped from 36.77 ± 0.5 to 36.13 ± 0.54℃ with TW and from 36.69 ± 0.36 to 35.98 ± 0.42℃ with PMF. Core temperature change over the whole protocol did not differ significantly between TW and PMF (−0.63 ± 0.56 versus −0.71 ± 0.38℃).

Separating the protocol phases, progress of all temperature parameters shows that an after chill occurred with both battings during the cool-down period from minute 63 to 84.5 (Figures 1(a), (b) and (e)). In this period TW caused less drop of body core temperature (−0.08 ± 0.22 versus −0.27 ± 0.3℃, p = 0.017) and skin temperature of the chest (−0.63 ± 0.71 versus −1.27 ± 0.83℃, p = 0.003, Figures 1(a) and (b)). This demonstrates that, due to the variation of the battings, temperatures took a different course after the activity. The absolute mean temperature value of the core and chest, however, did not differ significantly between both battings. OPEN IN VIEWER

Skin temperature of the upper arm was kept significantly higher with TW compared to PMF during both protocol phases (walking: 32.56 ± 1.12 versus 31.62 ± 1.23℃, p = 0.021; cool-down: 31.39 ± 1.27 versus 30.18 ± 1.3℃, p = 0.022).

Absolute humidity

Underneath the shirt and jacket absolute humidity increased during walking and decreased to a lower extent during cool-down (Figures 1(c) and (d)).

During the walking period absolute humidity increased underneath the shirt with TW from 12 ± 3 to 19.6 ± 5 g/m³ (from 34% to 58% RH) and with PMF from 13 ± 1 to 23 ± 5 g/m³ (from 39% to 68% RH) at the chest and with TW from 11 ± 3 to 17 ± 4 g/m³ (from 30% to 48% RH) and with PMF from 11 ± 2 to 21 ± 5 g/m³ (from 31% to 56% RH) at the back. TW caused less humidity and less rise of humidity underneath the shirt (chest: p = 0.002 and p = 0.003, back: p = 0.021 and p = 0.001) and jacket (chest: p = 0.002 and p = 0.003). In addition, a lower humidity was observed with TW underneath the shirt (chest: p = 0.001, back: p = 0.011) and jacket (chest: p = 0.001) also during the cool-down phase.

Surface temperature

At the start of the protocol, the surface temperature of the jacket dropped and remained stable until the end of walking (Figure 1(e)). Surface temperature was significantly higher with TW during walking (chest: p ≤ 0.001, back: p = 0.007) and resting (chest: p = 0.007).

Weight measurements

The use of TW and PMF resulted in a different sweat distribution within the two-layer outdoor clothing system (Table 2). TW absorbed more moisture and caused a lower sweat residue inside the long-sleeve shirt. Body weight loss (sweat production), evaporation, relative evaporation, and whole sweat residue (sum of the jacket, shirt, and soft shell pants) did not differ significantly between TW and PMF.

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Table 2.

Weight parameters. Values are presented as Mean ± SD, N = 12

Parameters	TW		PMF		p-values
	Mean	SD	Mean	SD
Body weight loss (g)	466	131	464	120	0.889
Evaporation (g)	396	84	399	68	0.799
Relative evaporation (%)	86.4	6.7	87.8	8.2	0.214
SR_jacket + shirt + pants (g)	54	44	49	45	0.386
SR_jacket (g)	31	19	19	15	0.001 a
SR_shirt (g)	19	23	27	27	0.043 a
SR_pants (g)	4	3	3	5	0.558

Stress level and comfort sensations

Heart rate and level of perceived exertion increased during walking and decreased during resting, but did not differ between TW and PMF. At the end of the walking period heart rates were 117 ± 8 and 114 ± 8 bpm with TW and PMF, respectively (Figure 2(a)), and load was perceived as very light (Figure 2(b)). Participants did not shiver and had no pain during testing. Thermal sensation changed from slightly warm to warm during walking and dropped from warm to slightly cool during the cool-down phase (Figure 2(c)). Thermal sensation was not significantly different between TW and PMF. Clothing felt scratchier during walking and less scratchy during resting (Figure 2(d)). Within the cool-down period clothing felt scratchier with TW compared to PMF (p = 0.035). OPEN IN VIEWER

After finishing the whole test protocol, participants made an additional assessment if they felt their thermal status comfortable during the whole test protocol. During the whole test protocol thermal state was felt acceptable by 10 of 12 participants with TW and 8 of 12 participants with PMF. The perceived thermal state of the whole test protocol did not differ significantly between TW and PMF.

Correlation analysis

Correlation analysis revealed significant correlations between absolute humidity and scratching and the thermal sensation (Table 3). Correlations were present especially at the end of the test protocol and mainly observed at the chest. The following correlations could be observed: the higher the humidity underneath the shirt the lower the sensation of scratch (the higher the comfort rating of scratching – 7 represented no sensation) and the higher the humidity underneath the shirt, the colder the thermal sensation.

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Table 3.

Correlations between absolute humidity underneath the shirt, scratching, and thermal sensation

Location	Time (min)	Absolute humidity and scratching				Absolute humidity and thermal sensation
		TW		PMF		TW		PMF
		r	p	r	p	r	p	r	p
Chest	0	0.532	0.075	0.272	0.393	0.181	0.573	0.154	0.634
	20	0.262	0.411	0.466	0.127	0.267	0.401	−0.105	0.745
	41.5	0.395	0.204	0.586	0.045 a	0.126	0.697	−0.590	0.043 a
	63	0.581	0.048 a	0.774	0.003 a	0.384	0.218	−0.702	0.011 a
	84.5	0.652	0.022 a	0.732	0.007 a	−0.558	0.060	−0.680	0.015 a
Back	0	0.518	0.085	0.184	0.567	0.116	0.721	0.090	0.781
	20	0.348	0.268	0.299	0.345	0.062	0.849	−0.304	0.336
	41.5	0.332	0.292	0.067	0.837	−0.124	0.700	−0.390	0.210
	63	0.493	0.103	0.314	0.320	0.232	0.468	−0.658	0.020 a
	84.5	0.565	0.056	0.491	0.105	−0.330	0.294	−0.681	0.015 a

Heat management

Particularly after physical activities in the cold it is of importance that clothing systems isolate the body well, counteracting an excessive cooling.^1,2 After walking in the cold with −5℃ ambient temperature, all temperature parameters dropped with both tested battings but core temperature did not decrease below 36℃ and, therefore, participants did not become hypothermic neither with TW nor with PMF. However, TW attenuated the core temperature and skin temperature drop after the activity. Water vapor and liquid sweat were transported more effectively from skin to the outer layer (Figure 3). This kept the skin more dry and warm and reduced the after chill effect. OPEN IN VIEWER

A higher surface temperature of the TW jacket was observed during the measurement. In general, this demonstrates that an increased heat transfer occurred between the clothing surface and the environment. This should have been resulted in a higher heat loss and lower skin and core temperatures of the wearer. Contrary to this expectation, skin and core temperatures were not lower wearing TW. The action of water vapor being absorbed by wool is classed as an exothermic reaction, thus providing a warming effect in the cold.^10,11

The higher surface temperature of the jacket might have indicated a heat-releasing effect of the wet batting and might have contributed to the lower temperature drop.

Moisture accumulated to a higher extent in TW, which will lead to a longer drying rate of the jacket. Obviously, the higher moisture accumulation did not strengthen the chilling effect after 20 minutes of walking at −5℃. It might be that this result would change with longer cool-down phases and should therefore be further reviewed.

Moisture management

Wu and Fan’s ⁹ material tests with different battings showed that wool, compared to polyester and down, was superior in terms of reducing moisture accumulation and increasing moisture transmission in the cold. Also in our investigation, using TW instead of PMF in the second layer of the two-layer outdoor clothing system effectively attenuated the rising humidity underneath the shirt and jacket and prevented moisture accumulation in the first layer during walking and resting in the cold. However, moisture accumulation in the second layer was higher with TW compared to PMF. The sweat production, whole sweat residue, evaporation, and relative evaporation were not significantly different between TW and PMF. These results imply that moisture transmission rates to the environment were almost similar with both battings, and a different moisture distribution within the two-layer clothing system occurred (Figure 3).

The additionally performed material tests indicated that TW had a lower water vapor resistance and higher air permeability. Therefore, we assumed that TW would show an improved moisture transfer throughout the jacket and a lower moisture accumulation inside the outerwear. Water vapor resistance and air permeability were measured in the dry state and might have been changed due to the strong absorption property of the wool during the measurement. Hes ²⁰ demonstrated that water vapor permeability of wool fabrics can change up to 70–80% when becoming wet. It could be that a fiber swelling and a compression of the fabric tissue took place whereby material properties changed and no longer differed between TW and PMF.

Comfort

Increased wetness in clothing systems and higher skin wetting are accompanied with worsened comfort sensations. In particular, thermal comfort and tactile sensations will be negatively influenced if skin becomes wet.^4,5 Wet skin causes a higher friction coefficient between skin and textiles. In addition, the skin friction coefficient can be more than twofold higher with wet fabrics compared to dry fabrics, which can result in skin irritations and discomfort. ⁶ Therefore, it was assumed that due to the improved moisture removal from the skin and lower humidity underneath the clothing system TW would have led to more pleasant comfort sensations. This assumption could not be confirmed. It was even perceived that the clothing felt scratchier with TW compared to PMF. It might be that the special fiber blend of the long-sleeve shirt composed of merino wool, elastane, and polyamide felt smoother when becoming slightly damp. The first layer, which was in direct contact with the skin, had the highest influence on the comfort sensations. The merino wool shirt and climate underneath the shirt were moister with PMF. The higher moisture content could have caused a smoother surface structure of the fabric tissue, resulting in a more comfortable tactile sensation with PMF. In this connection, a negative correlation could be observed that substantiates the following conclusion: the higher the absolute humidity underneath the shirt the lower the feeling of scratch. However, normally it is very unlikely that wool feels more comfortable when becoming wet because in wet states it opens its scales and increases its coefficient of friction. Obviously, the special fiber blend had a strong influence on this wool property, but it is necessary to verify these findings by further investigations.

A higher humidity can worsen thermal sensation in the cold. This was substantiated by an additional correlation that was only significant for PMF: the higher the absolute humidity the colder the feeling. That means that due to the higher moisture content, clothing should have felt colder with PMF than with TW, but this was not clearly confirmed because thermal sensation did not differ between the two battings. Therefore, moisture content was not high enough to influence thermal sensation negatively.

An additional interesting result was that correlations were primarily significant for the chest area. This indicates that comfort differences were more sensitively perceived on the chest than on the back area.