Thermal and Moisture Comfort Properties of Down Jacket Fabrics

TIAN YuanZHANG JunZHENG DongmingLIU ZhenruiZOU HaochenLIU JinkangDU Zhaoqun

1 College of Textiles，Donghua University，Shanghai 201620，China 2 Jiangxi Provincial Center for Quality Inspection and Supervision on Down Products，Gongqing 332020，China 3 Violet Home Textile Technology Co.，Ltd.，Nantong 226311，China

Abstract：In order to study the thermal and moisture comfort properties of down jacket fabrics，20 popular down jacket fabrics were selected from the market. The basic specifications of the samples were tested，and thermal and moisture performance tests were conducted. The obtained thermal and moisture indicators were analyzed，and then combined with the subjective evaluation results to obtain the regression equation for the evaluation of the comprehensive thermal and moisture comfort of down jacket fabrics. The air permeability，the thermal resistance，the warm and cold feeling and the moisture permeability were tested，and the results were divided into 5 levels. The results showed that the consistency of the air permeability and the moisture permeability of down jacket fabrics studied was better，and the thermal insulation of the down jacket fabrics with coating was better. The thickness of the down jacket fabrics had an effect on the warm and cold feeling of instant contact，and the consistency of subjective and objective warm and cold feeling was better. The obtained comprehensive evaluation equation of the thermal and moisture comfort has certain guiding significance for the thermal and moisture comfort of down jacket fabrics.

Key words:down jacket；fabric；thermal and moisture comfort；warm and cold feeling

Introduction

A down jacket is the main product in down products and one of the indispensable clothes for people to keep out the cold in winter.The existing research on down garments can be summarized into three kinds.The first one is the research on the warmth retention[1-6]，such as the influence of down filling and down content on the warmth retention of down garments；the second one is the structure of down and feathers[7]，and their fiber assembly[8]and the study of mixing with other waddings[9-10]are mostly related to warmth retention；the third one is the down drill[11]research.Comfort is related to physical properties and characteristics of fabrics and clothing，people’s activities，environmental conditions，and people’s physical and psychological factors.

Thermal and moisture comfort refers to the performance of fabrics between the human body and the environment which maintains and regulates heat and moisture transfer to stabilize the human body temperature and the appropriate humidity in the microenvironment.In 1941，Gaggeetal.[12]studied the thermal insulation performance of clothing from the perspective of human physiology，and proposed the thermal resistance and thermal insulation performance index CLO.In 1962，Woodcock[13-14]believed that sweat evaporation should also be considered for heat loss，and the moisture permeability index was introduced to describe the efficiency of fabrics in transferring moisture and related latent heat.In 1965，Goldman[15]combined CLO and the moisture permeability index to propose another index，namely the evaporative heat dissipation efficiency index.He believed that the three indices should be combined to evaluate the thermal and moisture comfort of fabrics.Regarding the research on the thermal and moisture comfort of fabrics，Zheng and Shen[16]found that when the thickness of the fabric increased，the CLO of the fabric would increase；the thicker the fabric was，the greater its moisture resistance and the worse its moisture comfort became.In addition，some scholars used the properties of fabrics[17-18]and algorithms[19-20]to study the thermal and moisture comfort of fabrics.

The researches on down jackets mostly focus on the inner down feathers and their influence on the warmth of the down jackets，but there are few studies on down jacket fabrics.Therefore，20 popular down jacket fabrics purchased from textile factories and markets，were evaluated in terms of the thermal and moisture comfort.

1 Experiments

1.1 Experimental conditions and instruments

(1)Test conditions.A laboratory with constant temperature and humidity is used，of which the temperature is (20±2)℃ and the relative humidity is (65±2)%.Before testing，the cut sample shall be balanced under the above standard conditions for 24 h.

(2)Instruments.The experimental instruments and their manufacturers are shown in Table 1.

Table 1 Experimental equipment

1.2 Basic parameters of samples

Before testing，the obvious wrinkles on the sample should be removed to keep the sample flat.The sample should be cut at least 15 cm from the edge of the cloth.After being cut，the sample with the tested surface is facing up，and the tested surface is the front of the fabric，i.e.，the finished fabric faces the outside.Table 2 shows the basic parameters of the samples.wandfrepresent yarn numbers per 10 cm in warp and weft directions measured by a mobile fabric density glass.Mrepresents the mass of the fabric per square meter by an electronic balance，anddrepresents the fabric thickness measured by the YG141 digital fabric thickness meter.

Table 2 Basic parameters of samples

1.3 Performance test

1.3.1Airpermeabilitytest

The fabric air permeability test adopts the YG461G automatic air permeability meter.Under a certain pressure difference，the air flows through the sample vertically in the measurement unit time.Under the same conditions，the air permeabilityRt(mm/s) of the sample is the average of the 10 test results：

(1)

whereVis the volume amount of air passing through the fabric in timet(s),mL;Ais the area of the fabric,cm2.

1.3.2Thermalresistancetest

The YG606E textile thermal resistance tester is used to test three indicators，which are thermal resistance，CLO and thermal conductivity.Fabric thermal resistanceRctrefers to the ratio of the temperature gradient difference between the two surfaces of the sample in a unit area to the heat flux passing through the sample vertically (including heat conduction，convection and radiation) in a given temperature field.The unit is m2·℃·W-1.Since thermal resistance，CLO and thermal conductivity can be converted mutually through formulae，we only discuss the thermal resistanceRcthere.It is the average of the test results of three samples:

(2)

whereTmis the surface temperature of the sample plate，℃；Tais the ambient temperature，℃；Acis the area of the test plate，m2；His the heating power provided to the test panel，W；ΔHcis the correction of the heating power in the thermal resistance measurement quantity；Rct0is the air thermal resistance measured in the blank experiment.

1.3.3Warmandcoldfeelingtest

The maximum instantaneous heat flowQmaxis tested by the KES-F7ⅡB contact heating and cooling sensation tester (shown in Fig.1)as the evaluation index to test the contact warm and cold feeling of down jacket fabrics.Qmaxrefers to the maximum instantaneous heat loss on the surface of the skin when the human skin contacts the fabric，i.e.，the maximum heat flow through the fabric，W/cm2.Qmaxis the average of 10 test results.

Fig.1 KES-F7ⅡB contact heating and cooling sensation tester

1.3.4Watervaporpermeabilitytest

The YG601H computerized fabric moisture permeability tester is used to test the moisture permeability WVT：

(3)

where WVT is the moisture permeability per square meter per day，g/(m2·d)；W1andW2are masses of the same experimental assembly before and after moisture permeability，g；Sis the test area of the sample，cm2；tais the test time，h.

1.4 Subjective heat and moisture evaluation

Six textile professionals are chosen to judge the thermal and humidity comfort of the samples by touching the samples in the constant temperature and humidity laboratory.Before the experiment，the definition of thermal and moisture comfort，the scoring standard and the method of touching the fabric are explained.Before touching the sample，each test participant needs to sit still in the laboratory for 20 min in order to adapt to the environment and adjust the personal mental state.Then，participants touch the control sample to familiarize themselves with the scoring criteria.

Subjective evaluation indices are divided into two parts：the instantaneous contact indexWfand the comprehensive thermal and moisture comfort indexCt.During the test，the front of the sample (the side away from the skin when the fabric is worn) should be placed on the arm.Wfis the warm and cold feeling within 5 s after the skin touches the fabric.It is divided into 1.0-5.0 points by the method of graded scoring (1.0 means strong contact cold feeling，and 5.0 means strong contact warm feeling).Ctis the feeling after putting the fabric on the inner arm for 1 min.The warmer，less stuffy and drier the skin of the down jacket fabric is，the more comfortable subjects feel.Ctis from 1.0 to 5.0.The higher the score is，the better the comprehensive thermal and moisture comfort performance is.

2 Results and Discussion

2.1 Subjective evaluation results

The samples were evaluated by six subjects and the results were averaged.The statistical results of subjective evaluation are shown in Table 3.

Table 3 Subjective evaluation results of thermal and moisture comfort

To prove the validity of the evaluation of six subjects，the Kendall consistency coefficientWwas calculated by SPSS and theχ2test was performed.According to Eqs.(4) and (5)，the consistency coefficients obtained were all significant at the 0.01 level.

(4)

χ2=m(n-1)W，

(5)

The Kendall consistency coefficient can effectively measure the consistency of the fabric handle level.The higher the value is，the better the consistency is.For the contact warm and cold sensation，Wis 0.904，andχ2is 103.051；the value of the comprehensive thermal and moisture comfortWis 0.927，andχ2is 105.723.It shows that the subjective evaluations of the six judges are effective，and their ranking values of 20 fabric samples can be used to represent the subjective evaluations.

2.2 Basic performance test results

The basic performance test of thermal and moisture comfort was carried out on 20 down jacket fabrics.The basic thermal and moisture index results of the fabrics are shown in Table 4.

Table 4 Basic thermal and moisture index results of down jacket fabrics

It can be seen from Table 4 that the air permeability of No.3 fabric is the highest.The air permeability of No.1 fabric is higher，about 106.91 mm/s.The air permeabilities of No.9，No.10，No.13 and No.19 fabrics are relatively high.In addition，the air permeability of most down jackets fabrics studied is 21.00-25.90 mm/s.For down jacket fabrics，fabrics with larger warp and weft densities have lower thickness and higher air permeability.Among the selected down jacket fabrics，most of the fabrics with low warp and weft densities are coated fabrics，so the thickness is relatively large and the air permeability is poor.The thermal resistance of the down jacket fabric is 0.021-0.044 m2·℃·W-1，the thermal resistance of No.6 fabric is the highest，and the thermal resistance of No.9 fabric is the lowest.The thermal resistance of coated or filmed down jacket fabrics is relatively large.In the water vapor permeability test of down jacket fabrics，No.3 fabric has the highest moisture permeability，and No.2 fabric has the lowest moisture permeability.The water vapor permeability test is performed on two sides of the down jacket fabric with a big difference between the front and the back，and the water vapor permeability test results of the down jacket fabrics with coatings or films are shown in Fig.2.

Fig.2 Moisture permeability of different down jacket fabrics on the front and the back

Most of the coated or filmed down jacket fabrics have little difference in moisture permeability between the front and the back，but there is a slight difference in the moisture permeability between the front and the back of No.4，No.5 and No.8 fabrics.By observing the reverse side of the down jacket fabric，it is found that No.4 fabric has a very bright coating，No.5 fabric has a thick coating on the back of the fabric，and No.8 fabric is a laminated structure.In general，the moisture permeability of coated down jacket fabric is poor，but the moisture permeability of No.5 fabric is better.The coating of No.5 fabric is thicker and smoother than other coated down jacket fabrics.

Winter clothing requires good wind resistance，heat insulation and warmth，so the lower the air permeability and the greater the thermal resistance are，the better the winter clothing is.When wearing down clothing，if sweat accumulates in the microenvironment between the clothing and the skin when human dissipates heat and sweats，the human body will feel uncomfortable.Therefore，the back of the down clothing fabric is the side close to the skin.Taken these 20 down jacket fabrics as a reference，the results are rated in Table 5.The higher the rating is，the better the performance is.

Table 5 Classification of basic thermal and moisture performance grades of down jacket fabrics

2.3 Contact warm and cold feeling results

Table 6 shows the test results of contact warm and cold feeling of 20 down jacket fabrics.

Table 6 Test results of warm and cold feeling through down jacket fabric contact

Qmaxof these 20 down jacket fabrics is 0.146-0.498 W/cm2，andQmaxof the most fabrics is 0.182-0.290 W/cm2.The thicknesses of No.2，No.3，No.4，No.13，No.17 and No.18 fabrics are relatively small，the path of heat passing is relatively short，and the heat is easier to lose through the fabric.ThusQmaxis high.A highQmaxindicates that the fabric has a strong instantaneous contact cold feeling.

In cold winter，the instantaneous contact temperature of the object will be lower.The stronger the warmth of instantaneous contact is，the better the comfort in winter is.In subjective evaluation，the stronger the warmth of the fabric is，the higher the score is.The lowerQmaxis，the stronger the warmth of contact is.It can be seen from Fig.3 that the subjective and the objective instantaneous contact warm and cold feelings have a good correlation，the Pearson coefficient is -0.801，and the adjustedR2is 0.641.These results show that through the objective test of the KES-F7ⅡB contact heating and cooling sensation tester，the contact warm and cold feeling of the fabric can be evaluated.The subjective and the objective evaluation values are analyzed，and Table 7 shows the classification of the contact warm and cold feeling.The higher the rating is，the better the performance is.

Fig.3 Subjective and objective evaluations of contact warm and cold feeling

Table 7 Classification of contact warm and cold feeling

2.4 Evaluation of Ct about down jacket fabrics

Combined the indicators of air permeability，thermal resistance，contact temperature and moisture permeability of down jacket fabrics with subjective comprehensive thermal and moisture comfort evaluation，the SPSS software is used to perform multiple linear regression analysis，and stepwise regression analysis is used to eliminate the effects on comprehensive thermal and moisture comfort.Thus an optimal or suitable regression model is established.

The results in Table 8 show that the adjustedR2increases with the increase of the number of variables in the model，wherex1is the air permeability rating value；x2is the thermal resistance rating value；x4is the moisture permeability rating value of the back of the fabric.In addition，the dependent variableyis the comprehensive heat and humidity comfort，x3is the maximum instantaneous heat flowQmax，andx3in the three regression models is eliminated.The correlation coefficient between the independent variable and the dependent variable is 0.942，the goodness of the fit valueR2is 0.888，and the adjustedR2value is 0.867.The analysis results of variance are shown in Table 9.

It can be seen from Table 8 that the significance of the three regression models fitted is less than 0.050，which is statistically significant.The respective variables are further tested.The regression analysis results are shown in Table 10.

Table 8 Summary of regression model

Table 9 Analysis results of variance

Table 10 Regression analysis results

Table 10 shows the results of each coefficient in the three models.The significances ofx1,x2andx4are all less than 0.050，and all of the three models are statistically significant.Therefore，the final regression equation is

y=1.214-0.365x4+0.552x2+0.411x1.

(6)

By substituting the rating value of each test result into Eq.(6)，F(xiàn)ig.4 shows a scatter plot of the comprehensive thermal and moisture comfort rating based on objective indicators and the subjective comprehensive thermal and moisture comfort rating to explain the relationship between the regression equation obtained above and the subjective test results.It can be seen from Fig.4 that they have a high linear correlation，with a Pearson coefficient of 0.933 and an adjustedR2of 0.870.These results also show that Eq.(6)has a great correlation with the subjective test results，and it can be used to evaluate the comprehensive thermal and moisture comfort of down jacket fabrics.

Fig.4 Subjective and objective ratings of comprehensive thermal and moisture comfort

3 Conclusions

In this paper，subjective and objective performance tests were carried out on the thermal and moisture comfort of down jacket fabrics.Coated or filmed fabrics in down jacket fabrics studied had large thermal resistance，good warmth retention，and low air and moisture permeability.The moisture permeability of the coated fabrics was also related to the smoothness and the evenness of the coating，and the coated fabrics were more suitable as the outer layer of the down jacket fabric.The down jacket fabric had a higherQmaxand a stronger cold feeling，because the down jacket fabric had a tighter structure and a smooth surface with less hairiness.The thinner down jacket fabric had a higherQmax，as the path of heat passing was relatively short，and the heat was easier to lose through the fabric，which was more suitable as the inner layer of the down jacket fabric.Based on subjective and objective test results,the multiple linear regression analysis was performed to obtain the regression equation for evaluating the comprehensive thermal and moisture comfort of down jacket fabrics，which was verified.It was proved that the regression equation was highly consistent with the subjective rating results，and the equation can be used to evaluate the comprehensive thermal and moisture comfort of down jacket fabrics，which provided a reference for related enterprises to quantitatively evaluate down jacket fabrics.