Insulating Effectiveness of Metallized Reflective Layers in Cold Weather Clothing Systems
ARMY RESEARCH INST OF ENVIRONMENTAL MEDICINE NATICK MA
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A physical analysis based on the laws of radiant energy transfer has been employed to indicate conditions under which metallized, reflective layers in fabric systems would be most likely to improve their insulating properties. This analysis suggests that such layers can be effective in reducing heat loss by radiation exchange through open-structured materials such as polyester batting, but have little potential when used in systems of densely-packed fibers or foam insulation, where radiation exchange is not a major factor. These indications were verified by insulation measurements, on a variety of polyester batting systems containing reflective layers of aluminum foil, metallized plastic films, or metallic foils bonded to cloth under pressure which fragmented the foil and made the reflective vapor permeable. Maximal effectiveness of reflectives was found when the systems were uncompressed, and had relatively thin batting layers with a metallic face next to each batting surface, i.e., two reflectives facing each other across every batt. It was shown that, in reality, uncompressed batting provided only about 70 as much insulation as conventional moderately dense fabrics, which allow little radiant heat loss reflectives simply minimized these losses in batting and made its thermal insulation per unit thickenss almost the same within 10 as for denser fabrics.
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