This research studied the relationship between heat transfer measured using a guarded sweating hot plate test method and the actual comfort and heat stress performance of firefighter turnout clothing. Controlled environment wear trials were conducted using the climate chamber available at the Center for Research on Textile Protection and Comfort (T-PACC) in the College of Textiles at North Carolina State University. Seven professional firefighters participated in these studies. Two different wear test protocols were performed to simulate two levels of work activity, climate conditions, and clothing and equipment variables: One protocol featured light to moderate work activity in a mild climate (21°C, 65% RH). Subjective and objective measures of human psychological and physiological response were applied to quantify and rate performance in several categories. A separate study was conducted to determine the heat stress experienced by firefighters performing moderate work activities in a warm environment (39°C, 35% RH).