Is your clothing comfortable? What are some of the factors that influence your answer with regard to the clothes that you are presently wearing?
It is likely that some of the textile characteristics of fabrics will influence your answer. It may also depend on how the garments fit or even on psychological factors, such as how you feel or whether you like the garments that you are wearing. Other factors that may influence your answer are whether you feel hot, cold, dry, or damp wearing these particular garments.
Physical phenomena affecting thermal comfort
Textiles serve as both a barrier and a transporter of heat, air, and moisture from one environment to another. In the case of clothing, apparel fabrics provide a boundary between the micro-environment immediately surrounding the body and the larger indoor or outdoor environment. In the case of interior furnishings fabrics, such as draperies, blankets, or carpets, textiles form the boundary between two larger environments. In either case, whether the fabric takes on the role of barrier or transporter depends on the physical characteristics of the textile and the differences in conditions such as temperature or moisture between the two environments.
1. Heat transfer
Heat transfer refers to the transfer of heat energy from one environment to another. Heat transfer occurs whenever a temperature difference (△ T) exists between the two environments; heat moves from the warmer surface or area to the cooler surface or area. Heat transfer will continue until the two areas are the same temperature (at equilibrium). The rate at which heat is transferred depends on △ T as well as any resistance imposed between the two environments. For people, this means that if the ambient temperature is lower than the body temperature (37 ° C), heat will flow from the body to the surrounding area. If the ambient temperature is higher than the body, heat will flow the other wav and the body will become warmer. Clothing can provide resistance to heat transfer in either direction by serving as insulation between the two environments.
2. Moisture transfer
Moisture transfer is another physical phenomenon that affects thermal comfort. Water is a much better heat conductor than air, and its presence lowers the effectiveness of a structure in preventing heat loss. Whether in liquid or vapor form, and whether produced by perspiration in a clothing assembly, high humidity in a room, or condensation in a commercial insulation application, moisture enhances heat transfer and reduces the effective r-value of a textile or a non-textile material.
3. Water Resistance
An area of concern for outdoor apparel and equipment manufacturers is the resistance of the outer fabric laver, or surface, to water penetration. The restriction of moisture transport can significantly affect comfort. Water-repellent apparel fabrics, such as rainwear, provide the desired comfort of protecting the wearer from the penetration of water through the fabric. However, in many fabrics, properties that provide water repellency may also restrict transfer of moisture vapor, resulting in the buildup of moisture near the skin due to perspiration. Microporous fabrics provide an effective solution to this problem. The pores in these fabrics are small enough to prevent the penetration of liquid water, which is several water molecules bonded together, but are larger than a molecule of water vapor. Thus, they provide both water repellency and a means of moisture vapor transport, keeping the wearer dry and comfortable.
4. Air permeability
ASTM D 737 is a widely used standard test method for air permeability. Using this method, a fabric specimen is placed on an air permeometer instrument and clamped so that the edges of the specimen are secured tightly against the machine. Compressed air is then forced through a known area of the fabric specimen. The rate of air flow is adjusted so that a prescribed pressure differential is achieved between the two sides of the fabric. The prescribed pressure differential is 12.7 mm of water, which is equivalent to 124 Pa.
Because comfort testing is so subjective, it is difficult to devise a test method to simulate this property. It is also usually easier to determine the different physical characteristics that contribute to comfort separately, rather than simultaneously. Several textile tests of properties that may contribute to the potential comfort of the wearer or user are described in this section.
Test methods for comfort related properties of textile fabrics
Air permeability of textile fabrics
Thermal transmittance of textile materials
Water vapor transmission of materials
Pore size characteristics of membrane filters using automated liquid porosimter
Absorbency of bleached textiles
Electrical resistivity of facrics
Electrical resistivity of yarns
Electrostatic clinging of fabrics: fabric to metal test
Electrostatic propensity of carpets