Impact of garment construction and environmental factors on heat transfer

Environmental factors and material construction parameters are both important considerations when evaluating the insulation performance of materials. The environmental factors of air layer thickness, wind speed, and ventilation are known to have a strong impact on insulation in fabric systems. This work builds on this knowledge by examining the interactions between these variables at different levels on various testing apparatuses- the small hot plate, the dynamic hot plate, and the heated torso. Additionally, the work assesses the effect of material air permeability and the influence on insulation at the various environmental conditions. A systematic approach revealed that material air permeability was primarily related to forced convective heat transfer and requires a minimum air layer thickness of 5 mm and wind speed of 1.3 m/s to be observed. Additionally, it was found that traditional methods of evaluating material thickness, such as ASTM D1777, apply a high force to the material and do not give an accurate measurement of uncompressed thickness- which is more indicative of what would be experienced during normal wear conditions. One sample in this study showed a difference > 2x when comparing the ASTM method to an alternative method (KES Compression Test) that applies a lower force, outlining the risk of inaccurate data.