# Alternative Method for Predicting Thermal Response in Two-Layer Systems
## 1 Introduction  
Protective clothing defends users from various toxic and environmental hazards [1, 2]. While protection against external hazards is paramount, there also exists serious concerns about the internal accumulation of heat. Clothing is responsible for both the heat exchange of the user with the environment and protection against ambient hazards [3, 4, 5]. When the clothing is not able to dissipate the heat generated by the user, numerous issues can arise, such as changes in the skin and core temperatures. This can eventually lead to potential life-threatening responses, such as heat stress and stroke [6, 7, 8]. Balancing the insulative properties of garments with the protective requirements is a delicate process [9]. Several aspects of the clothing and environment must be considered when evaluating the insulative properties. Previous studies have shown that the clothing fit and level of ventilation can have a significant impact on the total insulation provided by a clothing system [8, 10, 11]. [PERSON] et. found that the inner air layer, enclosed between the user and the garment, can account for up to 60% of the total insulation of a garment system [12]. In firefighter turnout, manipulation of the air layer thickness was found to prolong the time until burns occurred [2, 13]. Therefore, the material fit, and the subsequent microclimate thickness, have a significant impact on the insulation of garment systems. Similarly, other studies have found that ventilation via the garment and apertures also has a significant impact on the insulation [14, 15]. It has also long been accepted that the wind speed decreases the insulation of the garment system as it increases due to the \"stripping\" of the boundary air layer [16]. The critical impact of the environment on the insulation of garment systems is clear. Similarly, the construction and fibers of the garment itself are also important for heat exchange. [PERSON] et al. showed that polyethylene fabrics could be used to improve cooling [17], but typically, the fabric construction parameters have a strong impact on the insulation properties of garments. Namely, it was thought that the material thickness is the most influential construction parameter of fabrics [18]. But some studies have shownthat, in actuality, the air permeability of fabrics may be the most important construction parameter to consider [19; 20]. However, in these studies, the fabrics used were not only of various air permeabilities but also had discrepancies in their thicknesses. This made it difficult to determine whether the air permeability of these materials was the main influence on the insulation when the thickness was a confounding variable. But there has certainly been evidence that air permeability has a significant impact on insulation. Various test methods exist to predict the insulative performances of materials using various apparatuses, such as the heated sweating torso and sweating thermal manikin [21; 22; 23]. However, these tests are expensive and time-consuming. Therefore, one alternative test method is the sweating guarded hot plate. This test method is more convenient and uses less resources than the other ones mentioned, but it is not able to incorporate the environmental variables mentioned previously, such as the microclimate thickness and ventilation [24; 25]. Despite the mentioned limitations, the results from these insulation measurement systems can be used to predict human thermal responses using the human heat balance equation, which can then be used to determine the changes in human physiology over a given time and workload, and to predict the response of the user [26]. This is a powerful methodology, as it allows for predictions of the performances of various materials and scenarios [27; 28; 29]. Therefore, experiments were carried out using a modified guarded-hot-plate test in order to assess and compare the insulative properties of materials of differing air permeabilities but similar thicknesses.