Three prepared test specimens ( 6 x 6 in.) of each test item are submitted for testing. The thermal resistance of each sample is measured using the Indacore Stored Energy Test (SET) apparatus according to procedures similar to those provided in ASTM F1939 Standard test method for radiant protective performance of flame resistant clothing materials.

A bank of nine, 500 W infrared, tubular, translucent quartz lamps, provide the radiant heat exposure. The instrument is calibrated throughout testing to insure the delivery of a steady exposure at 2.0 cal/cm²·sec (8.4 watts/cm²).

The fabric sample is mounted in a sample holder positioned parallel with the heat source. An instrumented copper disk containing four iron/ constantan thermocouples measures heat transferred. This testing apparatus is limited to exposures of 60 seconds or less.