The comfort properties of newly developed 100% nylon and 100% polyester fabrics are compared with materials that are currently used in nuclear protective apparel, including a 100% cotton and a polyester/cotton fabric. The Kawabata Evaluation System provided a highly sensitive measure of fabric mechanical and surface properties. A sweating skin model measured heat and moisture transfer properties under various conditions of heat and humidity. Laboratory screening tests were followed by extensive studies to determine actual human reactions to the comfort of the new nylon and control materials and garments. Results of controlled climate chamber wear trials confirmed the overwhelming importance of environmental and work levels on comfort ratings. Before sweat generating exercise and in a moderate environment (21°C, 65%RH), the comfort of nylon coveralls was clearly preferred over identically designed garments made with 100% polyester, and with heavier weight 100% cotton or polyester/cotton fabrics. The comfort rating of all test garments dropped dramatically as wearers were put through an exercise routine, and as test conditions were changed to produce a hot and humid environment (32°C, 90%RH). However, even under more stressful conditions, the comfort of the light weight nylon coverall was preferred over the controls in most cases. The higher absorption capacity of the cotton fabrics was beneficial in comfort comparisons made by the evaluators in a hot and humid environment.