Effects of simulated sustained operations on the thermal insulation of military footwear

This study investigated the effects of a simulated environmental exposure on the thermal insulation of an improved version of a military boot designed for use in cold and wet environments. A thermal foot model (TFM) measured total boot and localized (toes and heel) thermal resistance (R, m2·K·W−1) values of the standard (non-removable insulation) and the new version (removable/replaceable insulation bootee) of the US Army Intermediate Cold Wet Boot (ICWB). The 5-day test consisted of three phases: day 1 where the boot was tested on the heated (30°C) TFM in a dry condition to establish initial R values at a chamber temperature and relative humidity of 20°C and 25%, respectively; day 2 where the boot was externally wetted for 24 h while standing in 10 cm of water with the temperature and humidity increased to 25°C and 50%, respectively; and days 3–5 where the water was removed and the boot was evaluated at day 1 conditions. Initial TFM R values for the total boot show no significant difference between the standard (0.203) and newer version (0.192) of the ICWB. The 24-h water exposure however, resulted in a reduction of 60% of the standard boot's initial R compared to a 35% reduction for the new boot. Furthermore, the water exposure caused significantly higher R losses in the toe (74%) and heel (72%) regions when compared to the new boot (54% and 49%, respectively). At the end of day 5, the standard boot had regained 94% of initial R compared to a 100% regain for the new boot. Initial dry weights of the standard and new boots were 1.02 and 1.19 kg, respectively. Water exposure increased the weight of the standard boot by 23% compared to a 14% increase for the new boot. At the end of day 5, the standard boot still retained 4% of the absorbed water while the new boot had completely dried, returning to initial weight. Although the new ICWB was slightly heavier, it absorbed less water during a 24-h wetting, retained more insulating ability when wet, and dried more completely than the standard ICWB.