The torso cooling of vests incorporated with phase change materials: a sweat evaporation perspective

Abstract

Cooling vests incorporated with phase change materials (PCMs) add extra insulation and restrict sweat evaporation. It is still unclear how much cooling benefit they can provide. The aim of this study was to investigate the torso cooling of the PCM vests in two hot environments: hot humid (HH, 34°C, 75% relative humidity (RH)) and hot dry (HD, 34°C, 37% RH). A pre-wetted torso fabric skin was used to simulate torso sweating on a thermal manikin. Three cooling vests incorporated with three melting temperatures (T_m) of PCMs were tested (T_m = 21°C, T_m = 24°C and T_m = 28°C). They were worn under a military ensemble (total thermal insulation 1.60 clo; evaporative resistance 0.0516 kPaċm²/W), respectively. In a HH environment all the three cooling vests provided effective torso cooling; in a HD environment the cooling benefit was negative. In both environmental conditions, the evaporative cooling was greatly restricted by the cooling vests. The study indicated that when wearing the protective clothing with the relatively low evaporative resistance and when sweat production was high, the cooling vests were effective in a HH environment, but not in a HD environment.

Keywords

cooling phase change material evaporation protective clothing

Industrial workers, military personnel and firefighters are often exposed to heat stress in work environments.^1–6 In order to protect them from the extreme heat, harmful particles and other potential injuries, they must wear special protective clothing. Sweat evaporation may be the only way for them to lose heat in hot environments, but the highly insulated protective clothing impedes the sweat evaporation and contributes to heat stress.^2,6,7 According to ISO 7243, an essential requirement for work in hot environments in occupational settings is that the body core temperature may not exceed 38°C in a work period.⁸ Above that, the risk for hyperthermia and related heat disorders may occur and threaten workers’ safety and health.^2,3

In order to achieve heat equilibrium and maintain the body core temperature within a safe range, various cooling garments have been developed to reduce heat strain, such as liquid cooling garments,^9–11 compressed air cooled garments^4,12 and ventilated cooling garments.^13–15 These cooling methods are classified as active cooling systems.¹⁶ Cooling vests using passive cooling resources, such as ice,^17,18 frozen gels^19–21 and other phase change materials (PCMs) (e.g. paraffin and salts)^{16,18,22–24} have also been developed. They can be conveniently incorporated into clothing without any external connections. Thus, they have been extensively applied as a countermeasure to alleviate heat strain together with protective clothing^16,18,19,22 in sports and exercise,^17,20,21 and in outdoor physical work in hot climates.²³

Many investigations on PCM vests have been carried out on either human subjects or thermal manikins. Chou et al.¹⁸ conducted a subject wear trial using an ice vest, a vest containing PCM5 with a melting temperature (T_m) of 5°C, and a vest containing PCM20 (T_m = 20°C) under firefighters’ protective clothing in a moderately hot environment (30°C, 50%RH). The subjects who did not wear the cooling vests felt hotter and wetter than those who did. The PCM vests were reported to be more effective for cooling than the ice vests. Choi et al.²³ examined the cooling effects of various combinations of PCMs incorporated in different garment pieces – a scarf, a hat and a vest – under a simulated red pepper harvest at WBGT (wet bulb globe temperature): 33°C. The subjects’ rectal temperatures were effectively maintained below 38°C. When the head, neck and torso were covered by pieces of PCMs, the subjects’ mean skin temperature and heart rate were reduced to the comfort level. The authors suggested that a 3.3% cooling area of the body was effective in alleviating the heat strain. In contrast, Brade et al.²¹ examined the cooling effect of a PCM17 (T_m = 17°C) jacket and a gel jacket (gels were formed in 2–5°C icy water) used in post exercise. They reported that there was no cooling benefit for either one. Gao et al.^16,24 investigated PCM vests worn under firefighters’ protective clothing using both a thermal manikin and human subjects. The cooling effects of different melting temperatures of PCMs were investigated. It was observed that the larger the temperature gradient between the melting temperature of the PCMs and the manikin surface temperature, the stronger the cooling effect. PCM vests with lower melting temperatures more effectively cooled human subjects. Bendkowska et al.²⁵ evaluated three cooling vests incorporated with different micro-capsulated PCMs on a dry-heated thermal manikin. The microcapsules of PCMs with a weight of 2.3 kg were encapsulated into sacks and then were inserted into the vests. Two vests were incorporated with 100% hexadecane (T_m = 18°C) and 100% octadecane (T_m = 28°C). The third vest was incorporated with a mixture of 50% hexadecane and 50% octadecane (T_m was between 10 and 34°C) and was reported to have the best cooling effect.

The above-mentioned physical activities and working environments usually require high levels of oxygen (O₂) uptake and energy expenditure.^4,7,17 The weight of the protective clothing adds much load to the wearers and affects their working performance and productivity.²⁶ The vests with the incorporated cooling materials result in extra load for the wearers. To reduce the weight of the cooling vest while preserving efficient cooling benefit, some researches have suggested lightweight cooling vests.^27–29 Still another problem of the cooling vests incorporated with these materials needs to be mentioned. The added layers of the vests together with the cooling materials increase the evaporative resistance of the clothing ensemble and can greatly depress the evaporative cooling power.

For the assessment of personal cooling systems, a sweating heated thermal manikin was recommended as a convenient tool by the ASTM F2371 standard.³⁰ The sweating heated manikin provides objective and repeatable results. Since almost all previous research has focused on the whole body cooling effect, very few studies have been carried out that examine torso cooling and the negative effects on it due to the introduction of the vests. Therefore, the aim of the study was to investigate whether PCM vests could provide torso cooling benefits under the protective clothing in both hot dry (HD) and hot humid (HH) environments. A sweating heated thermal manikin was used to test the PCM vests. It was hypothesized that the cooling vests would reduce evaporative cooling and would not provide any cooling benefit in the two hot environments.

Methods

Clothing tested

Three commercially available cooling vests incorporated with PCMs (TST Sweden AB) were used in this study. The vests were of the same size and design structure and were made of the same fabrics (Figure 1). They were tested under a military ensemble (MIL) (produced by Taiga AB, Sweden), including a short-sleeve T-shirt and briefs.

Figure 1.

The cooling vest incorporated with phase change material packs.

The main ingredients of the PCMs were salt mixtures, including sodium sulfate and water, known as Glauber’s salt.^16,24 They were encapsulated into 21 small packs and were inserted into the pockets of the vests (Figure 1). Three different melting temperatures of the PCMs were used in the three vests: PCM21 (T_m = 21°C), PCM24 (T_m = 24°C) and PCM28 (T_m = 28°C). Descriptions of the experimental clothes are provided in Table 1. All three cooling vests were kept at 15°C overnight so the PCMs would solidify before use.³¹

Table 1.

Descriptions of the experimental clothes

Code	Clothing component	Total thermal insulation (clo)	Evaporative resistance (kPaċm²/W)	Permeability index (non-dimensional)	Total weight (kg)
MIL	Polyamide/cotton jacket, polyamide/cotton long trousers, short sleeve T-shirt, briefs	1.60	0.0516	0.322	1.146
VE21	Polyester vest, 21 PCM packs (T_m = 21°C; latent heat of fusion: 144 J/g; PCM weight: 1.806 kg; total heat of fusion: 260 kJ; dimension of each pack: $13 cm \times 7 cm \times 1 cm$ ; cooling area: 0.19 m²)	0.749	0.0405	0.191	2.218
VE24	Polyester vest, 21 PCM packs (T_m = 24°C; latent heat of fusion: 106 J/g; PCM weight: 1.730 kg; total heat of fusion: 183 kJ; dimension of each pack: $13 cm \times 7 cm \times 1 cm$ ; cooling area: 0.19 m²)	0.750	0.0402	0.192	2.142
VE28	Polyester vest, 21 PCM packs (T_m = 28°C; latent heat of fusion: 159 J/g; PCM weight: 1.746 kg; total heat of fusion: 278 kJ; dimension of each pack: $13 cm \times 7 cm \times 1 cm$ ; cooling area: 0.19 m²)	0.759	0.0377	0.209	2.158

Note: the thermal insulation of the military ensemble (MIL) was measured with all the clothing pieces worn on the thermal manikin. The evaporative resistance of the military ensemble was measured using a coverall fabric skin.^32,33 The thermal insulation of the cooling vests was measured with only the cooling vests worn on the manikin. The evaporative resistance of the cooling vests was measured by using a torso fabric skin, since only the torso was covered (Figure 2). The thermal insulation of the cooling vests was measured at the following ambient temperatures: 21°C for VE21, 24°C for VE24 and 28°C for VE28. The relative humidity and air velocity were 50% and 0.4 m/s. The manikin surface temperature was kept at 34°C. The evaporative resistance of the cooling vests was measured at an ambient temperature of 34°C, 60% relative humidity (RH) and 0.4 m/s air velocity. Since the phase change materials (PCMs) absorb heat while melting, they will influence the real thermal insulation and the real evaporative resistance of the cooling vests. Hence, after the incorporated PCMs melted completely, the measurements of the thermal insulation and the evaporative resistance of the three cooling vests were carried out.

The thermal manikin and the torso fabric skin

A dry-heated thermal manikin, Tore, with 17 independent controlling zones was used to assess the cooling vests.^24,31 A torso fabric skin (100% cotton knitted, area weight: 135 g/m²) that fitted Tore tightly was used to simulate the torso sweating. The fabric skin covered four zones: the chest, belly, back and buttocks (Figure 2). It was pre-wetted with tap water to simulate sweat-saturated skin.^32,33 The moisture content in the fabric skin was about 147% of the initial weight.

Figure 2.

Torso fabric skin on Tore.

Ambient condition

The climate chamber’s ambient temperature was controlled at 34°C and the air velocity at 0.4 m/s. Two humidity conditions were tested: HH and HD. The HH condition was set at a relative humidity (RH) of 75% (corresponding to 4 kPa of water vapor pressure). The HD condition was set at a RH of 37% (corresponding to 2 kPa of water vapor pressure). The manikin surface temperature was kept the same as the temperature of the climate chamber.^24,29

Testing protocol

In both environmental conditions, five measurement scenarios were tested: Fabric Skin (the fabric skin only), MIL (military ensemble without the cooling vest, a baseline), MIL21, MIL24 and MIL28 (military ensemble together with the cooling vests incorporated with PCM21, PCM24 and PCM28, respectively).

In each scenario, a weighing scale (accuracy: ±2 g, Mettler Toledo, Switzerland) was used to determine the real-time mass loss rate of the sweat vapor leaving the manikin clothing system³⁴ (Figure 3). The real-time mass loss was recorded by the scale’s software program at 10-second intervals. The manikin controlling system recorded the heat loss, as well as the manikin surface temperature every 10 seconds. Each test was repeated three times and the average values were calculated for the analysis. Only the four zones covered by the torso fabric skin were included to calculate the torso heat loss.

Figure 3.

The whole manikin clothing system.

Results

The cooling power of the whole torso over time in the various conditions is illustrated in Figure 4. In the HH condition, the dynamic heat losses of the whole torso brought about by the three cooling vests were all significantly higher than the baseline condition during the 1-hour period. In contrast, in the HD condition, all three cooling vests had no conspicuous cooling effect compared to the baseline condition. In both humidity environments, the heat removal rate (the slope of the curves excluding the peak values in the initial test period) for the three cooling vests followed the trend MIL21 > MIL24 > MIL28.

Figure 4.

The torso cooling power of the baseline and the vest scenarios over time: (a) in the hot humid condition; (b) in the hot dry condition. (Note: The torso heat loss was area weighted by the four covered zones. The manikin torso area is 0.57 m². The torso fabric skin was assumed to have the same area as the manikin torso, as it was thin and fitted the manikin tightly. The torso heat losses of the Fabric Skin scenarios were not included in the figures, since the cooling power in a simulated nude situation was not of interest in the study, but the results are listed in the tables as a reference for discussion).

Tables 2 and 3 summarize the total torso cooling power and the evaporative cooling power in the HH and the HD conditions, respectively. Compared with the low humidity in the HD, the high ambient humidity in the chamber was more difficult to control. Hence, the deviations of the results between each test in the HH condition were higher.

Table 2.

The torso cooling power under the hot humid (HH) condition

Code	In HH
Code	HLtorso (W/m²)	ΔHLtorso (%)	$\frac{d m}{d t}$ (g/h)	E (W/m²)	ΔE (%)
Fabric Skin	72 ± 7	–	80 ± 8	95 ± 10	–
MIL (baseline)	26 ± 1	–	23 ± 1	27 ± 2	–
MIL21	52 ± 2	100	9 ± 0.4	11 ± 0.5	−59
MIL24	46 ± 3	77	10 ± 0.1	12 ± 0.2	−56
MIL28	41 ± 2	58	16 ± 1	19 ± 2	−30

Table 3.

The torso cooling power under the hot dry (HD) condition

Code	In HD
Code	HLtorso (W/m²)	ΔHLtorso (%)	$\frac{d m}{d t}$ (g/h)	E (W/m²)	ΔE (%)
Fabric Skin	186 ± 9	–	217 ± 3	256 ± 3	–
MIL (baseline)	79 ± 0.4	–	77 ± 2	91 ± 3	–
MIL21	80 ± 2	1	38 ± 2	45 ± 3	−51
MIL24	75 ± 1	−5	39 ± 2	46 ± 3	−49
MIL28	73 ± 3	−8	41 ± 1	48 ± 1	−47

Note: in both Tables 2 and 3, the values were average values for the stable period (the period after the manikin system stabilized and before the fabric skin began to dry). The ratio of $\frac{d m}{d t}$ is the evaporative rate of the moisture from the wet fabric skin leaving the manikin clothing system. E is the evaporative heat loss and is calculated by the following formula: $E = \frac{1}{A} \cdot λ \cdot (\frac{d m}{d t})$ . λ is the heat of vaporization of water at the measured skin temperature. In the study, λ was 0.673 Wċh/g at 34°C.³³ A is the area of the wetted torso fabric skin. In both environmental conditions, ΔHL_torso and ΔE were calculated by the comparison with the baseline scenarios.

As shown in the tables, when the manikin was covered only with the fabric skin, the torso heat loss and the evaporative rate were the highest among all the five scenarios. When the military ensemble was worn over the fabric skin in both humidity conditions, the cooling power was greatly reduced. The reductions were 64% and 58% in HH and in HD, respectively. When the cooling vests were introduced under the military ensemble, the torso heat loss in HH increased by 100% for MIL21, 77% for MIL24 and 58% for MIL28. However, no significant cooling effect was observed in the HD condition. The three cooling vests brought negative effect. In both humidity conditions, the sweat evaporation was greatly restricted after the cooling vests were added.

Discussion

PCM vests as a heat stress countermeasure have been developed in the past few decades. Many researches have demonstrated their positive effect on alleviating heat strain in protective clothing,^16,18,19,28 but a potential negative effect of the extra evaporative resistance to the wearers has not yet been reported. For humans, sweat evaporation is a powerful cooling mechanism in hot environments.² This study, therefore, investigated the cooling benefit of PCM vests from another perspective that focused primarily on the evaporation cooling.

In the HH condition, the evaporative heat loss for the MIL (baseline) was greatly hindered. The low water vapor pressure gradient between the fabric skin surface and the ambient environment made evaporation difficult. When the protective clothing was worn, the powerful cooling mechanism of evaporation could not fully function and thus the heat loss was small. When other protective clothing with higher evaporative resistance is worn, such as firefighters’ protective clothing, the sweat evaporation is even more depressed in HH environments.^2,6 The cooling vests in this situation could provide an additional cooling mechanism by means of conductive heat loss.

For the three cooling vests worn under the military ensemble in HH, the torso cooling benefits were all positive. They increased the heat loss from the torso by 100% for MIL21, 77% for MIL24 and 58% for MIL28. Hence, the cooling vests were effective for use in such a hot and humid condition under protective clothing. When the ambient humidity was even higher and the evaporative resistance of the protective clothing was higher, the evaporative cooling power was even weaker and the PCM vests could provide a much higher cooling benefit. Moreover, the cooling rate of the three vests differed, with the MIL21 providing the highest cooling effect, followed by the MIL24 and the MIL28. This is in agreement with previous studies of Gao et al.^16,24 The incorporated PCMs for the three vests covered the same body area and their weight made very little difference. The significant difference was their melting temperatures. Because of the larger temperature gradient between the manikin surface and the melting temperature of the PCM21, the driving force for heat removal was stronger.

However, the evaporative cooling in HD could function much better without a cooling vest. When the military ensemble was worn in that condition, the heat loss by evaporation (79 W/m² for MIL in HD) was much higher than that in the HH condition (26 W/m² for MIL in HH). When the cooling vests were added under the military ensemble, the PCM cooling capability could not compensate for the restricted evaporation cooling due to the increased evaporative resistance. The combined cooling effect from both PCMs and the evaporation was smaller than that in the MIL situation. Therefore, they are not recommended for use under military ensembles in hot and dry environments and in conditions where sweat production is high but the evaporative resistance of the protective clothing is low; otherwise, the cooling vests just add extra insulation, evaporative resistance and load to the wearers, resulting in the negative effect.

Similar results of PCM vests in human trials were reported in research conducted by Carter et al.²² A PCM cooling vest with T_m = 28°C was tested under a gas-tight suit at an ambient environment of 16.5 ± 1.8°C and 44 ± 3% RH. It was reported that no cooling benefit was observed. In their study, the tests were carried out at a relatively low ambient temperature, where the PCMs might not melt completely. On the other hand, the ambient humidity was moderately low and evaporation cooling in the baseline situation could have played an effective role. This was close to the HD condition in the study presented here, which was performed on a thermal manikin. The results obtained may not be comparable with those from human subjects, but can be validated to a certain extent by their findings. Both studies indicate that the PCM vests should not be used in a dry or moderately dry environment.

In real work environments, metabolic heat production is increased with work intensity. The load of the protective clothing can also increase heat production.⁷ The added cooling vest could further increase the load, in which case the real cooling benefit would decline. The effect of the extra load could not be assessed by a thermal manikin, which was one limitation of the study. Moreover, the human body might compensate for the reduced torso sweat evaporation by increased sweating elsewhere and thus evaporation elsewhere, in which case the real restriction of evaporation would be smaller.

It was inevitable that the evaporative cooling power would be reduced by the added vest layers and the cooling materials. In both humidity conditions, these cooling vests restricted the evaporative rate greatly and resulted in the reduction of evaporative cooling (Table 2 and 3). For evaporative cooling, only the sweat vaporized at the skin surface can deliver the maximal cooling effect. When multi-layered protective garments are worn, the site of phase change of water is remote from the skin surface and the cooling effect is reduced.³⁵ This problem may be solved by the structure design of the vest and PCM packs, for instance, by encapsulating the PCMs with a honeycomb pattern to increase the water vapor permeability.³⁶

Conclusions

In this study, the torso cooling of three PCM vests worn under military ensembles was investigated in two environmental conditions, HH and HD. When the cooling vests were introduced in a HH condition, the torso heat loss increased by 100% for the MIL21, 77% for the MIL24 and 58% for the MIL28. By contrast, in a HD condition, the torso heat loss increased by 1% for the MIL21, decreased by 5% for the MIL24 and decreased by 8% for the MIL28. Therefore, when wearing protective clothing with relatively low evaporative resistance and when sweat production was high, the PCM vests were effective in the HH condition, but not in the HD condition.

Footnotes

Acknowledgment

The authors are grateful to Eileen Deaner for language editing.

Funding

This work was supported by the the National Natural Science Foundation (51106022), Innovation Program of Higher Shanghai Municipal Education Commission (12ZZ068), the Fundamental Research Funds for the Central Universities (11D10715) and Doctoral Students Research Program supported by Donghua University (BC201116).

References

Epstein

Moran

. Thermal comfort and heat stress indices. Ind Health 2006; 44: 388–398.

Nunneley

. Heat stress in protective clothing: Interactions among physical and physiological factors. Scand J Work Environ Health 1989; 15: 52–57.

Barr

Gregson

Reilly

. The thermal ergonomics of firefighting reviewed. Appl Ergon 2010; 41: 161–172.

Barwood

Newton

Tipton

. Ventilated vest and tolerance for intermittent exercise in hot, dry conditions with military clothing. Aviat Space Environ Med 2009; 80: 353–359.

Holmér

. Protective clothing and heat stress. Ergonomics 1995; 38: 166–182.

Holmér

Kuklane

Gao

. Test of firefighters’ turnout gear in hot and humid air exposure. Int J Occup Safety Ergon 2006; 12: 297–305.

Dorman

Havenith

. The effects of protective clothing on energy consumption during different activities. Eur J Appl Physiol 2009; 105: 463–470.

ISO 7243. Hot environments-estimation of the heat stress on working man, based on the WBGT-index (wet bulb globe temperature), Geneva, International Standards Organization, 2003.

Kayacan

Kurbak

. Effect of garment design on liquid cooling garments. Textil Res J 2010; 80: 1442–1455.

10.

Kim

LaBat

. Design process for developing a liquid cooling garment hood. Ergonomics 2010; 53: 818–828.

11.

Barwood

Davey

House

. Post-exercise cooling techniques in hot, humid conditions. Eur J Appl Physiol 2009; 107: 385–396.

12.

Kuklane K, Holmér I, Ohlsson G, et al. Heat stress in ventilated air tight coverall. In: Werner J and Hexamer M (eds) In: proceedings of the 9th international conference on environmental ergonomics (ICEE), vol. 4, Shaker Verlag, Dortmund, 2000, pp.361-364.

13.

Gonzalez

. Determination of the cooling capacity for body ventilation system. Eur J Appl Physiol 2011; 111: 3155–3160.

14.

Hadid

Yanovich

Erlich

. Effect of a personal ambient ventilation system on physiological strain during heat stress wearing a ballistic vest. Eur J Appl Physiol 2008; 104: 311–319.

15.

Chinevere

Cadarette

Goodman

. Efficacy of body ventilation system for reducing strain in warm and hot climates. Eur J Appl Physiol 2008; 103: 307–314.

16.

Gao

Kuklane

Holmér

. Cooling vests with phase change materials: The effects of melting temperature on heat strain alleviation in an extremely hot environment. Eur J Appl Physiol 2011; 111: 1207–1216.

17.

Arngrímsson

SÁ

Petitt

Stueck

. Cooling vest worn during active warm-up improves 5-km run performance in the heat. J Appl Physiol 2004; 96: 1867–1874.

18.

Chou

Tochihara

Kim

. Physiological and subjective responses to cooling devices on firefighting protective clothing. Eur J Appl Physiol 2008; 104: 369–374.

19.

Bennett

Hagan

Huey

. Comparison of two cool vests on heat-strain reduction while wearing a firefighting ensemble. Eur J Appl Physiol 1995; 70: 322–328.

20.

Webster

Holland

Sleiverts

. A light-weight cooling vest enhances performance of athletes in the heat. Ergonomics 2005; 48: 821–837.

21.

Brade

Dawson

Wallman

. Postexercise cooling rates in 2 cooling jackets. J Athl Train 2010; 45: 164–169.

22.

Carter

Rayson

Wilkinson

. Strategies to combat heat strain during and after firefighting. J Therm Biol 2007; 32: 109–116.

23.

Choi

Kim

Lee

. Alleviation of heat strain by cooling different body areas during red pepper harvest work at WBGT 33°C. Ind Health 2008; 46: 620–628.

24.

Gao

Kuklane

Holmér

. Cooling vests with phase change material packs: the effects of temperature gradient, mass and covering area. Ergonomics 2010; 53: 716–723.

25.

Bendkowska

Klonowska

Kopias

. Thermal manikin evaluation of PCM vests. Fibres Text East Eur 2010; 18: 70–74.

26.

Louhevaara

Ilmarinen

Griefahn

. Maximal physical work performance with European standard based fire-protective clothing system and equipment in relation to individual characteristics. Eur J Appl Physiol 1995; 71: 223–229.

27.

Nishihara

Tanabe

Hayama

. A cooling vest for working comfortably in a moderately hot environment. J Physiol Anthropol Appl Hum Sci 2002; 21: 75–82.

28.

Reinertsen

Farevik

Holbo

. Optimizing the performance of phase-change materials in personal protective clothing systems. Int J Occup Safety Ergon 2008; 14: 43–53.

29.

Smolander

Kuklane

Gavhed

. Effectiveness of a light-weight ice-vest for body cooling while wearing fire fighter’s protective clothing in the heat. Int J Occup Safety Ergon 2004; 10: 111–117.

30.

ASTM F2371. Standard test method for measuring the heat removal rate of personal cooling systems using a sweating heated manikin, West Conshohocken, 2010.

31.

Gao C, Kuklane K and Holmér I. Thermoregulatory manikins are desirable for evaluations of intelligent clothing and smart textiles. In: proceedings of the 8th international meeting on thermal manikin and modeling (8I3M), Victoria, Canada, 2010, pp.1–5.

32.

Wang

Kuklane

Gao

. Effect of temperature difference between manikin and wet fabric skin surfaces on clothing evaporative resistance: how much error is there? Int J Biometeorol 2012; 56: 177–182.

33.

Wang

Gao

Kuklane

. Determination of clothing evaporative resistance on a sweating thermal manikin in an isothermal condition: heat loss or mass loss method? Ann Occup Hyg 2011; 55: 775–783.

34.

Wang

Gao

Kuklane

. A study on evaporative resistances of two skins designed for thermal manikin Tore under different environmental conditions. J Fiber Bioeng Inform (JFBI) 2009; 1: 301–305.

35.

Craig

Moffitt

. Efficiency of evaporative cooling from wet clothing. J Appl Physiol 1974; 36: 313–316.

36.

Wang

. Characterization on pore size of honeycomb-patterned micro-porous PET fibers using image processing techniques. Ind Textila 2010; 61: 66–69.