This paper describes an interlaboratory study conducted using ASTM F2731, Standard Test Method for Measuring the Transmitted and Stored Energy of Firefighter Protective Clothing Systems. Five replications of six different composites representative of firefighting turnout gear materials were tested at six different laboratories equipped to conduct the test. Data collected were used to predict the time to second degree burn for each of the turnout composite test specimens. Statistical analysis showed good agreement between test sites. This interlaboratory study confirmed the repeatability and reliability of ASTM F2731, a test method used to measure an important property associated with the thermal protective performance of firefighter turnout materials.