Thermal conductivity K is a parameter used to characterize the thermal conductivity of a substance. It is one of the basic physical properties of a substance. The smaller the value, the worse the thermal conductivity of the substance and the better the thermal insulation. The heat conduction system of various textile materials is shown in the table below. Table 1 Thermal conductivity of textile materials (measured at room temperature 20°C) Material K (W/m·°C) Material K (W/m·°C) Cotton 0.071～0.073 Polyester 0.084 Wool 0.052～0.055 Acrylic 0.051 Silk 0.050～0.055 Polypropylene 0.221～ 0.302 viscose fiber 0.055～0.071 spandex 0.042 acetate fiber 0.050 air 0.026 nylon 0.244～0.337 water 0.697 It can be seen from Table 1 that the thermal conductivity of still air is the smallest and is the best thermal insulator. Under normal circumstances, the thermal conductivity of textile materials that we don’t have is actually the thermal conductivity of a mixture of fiber, air and moisture, and the porosity of the fabric is generally 70% to 80%, so the thermal insulation of textile materials is great. The extent depends on the state and amount of air trapped in the fiber layer. Under the premise of non-flowing air, the more air held in the fiber layer, the better the warmth retention of the fiber layer. Therefore, the fabric is soft, thick, and contains a lot of air, and it has good warmth retention. The napped pile fabric has better warmth retention than ordinary fabrics, and it is also because a certain thickness of air layer is maintained between the piles. However, once the air in the fabric flows, the warmth and heat insulation properties of the fabric are greatly reduced. The thermal conductivity of water is relatively large, about 10 times that of general textile materials, and approximately 30 times that of air. Therefore, water has a great influence on the warmth retention of the fabric. Generally speaking, after the fabric is wetted, the thermal conductivity of the fabric will increase and the warmth retention will decrease. More about thermal protection performance test
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