This study was intended to support the development of new test technology and requirements for possible inclusion in the 1997 edition of NFPA 1971, Standard on Protective Ensemble for Structural Fire Fighting. The particular focus of this study was to examine test methods related to the thermal protection of fire fighter protective clothing. Both conductive heat resistance and radiant heat resistance performance areas were investigated for a number of composites and compared with thermal protective performance test results. Conductive heat resistance testing was conducted using Test Method F 1060 while radiant heat resistance testing was performed using procedures in NFPA 1976, Standard on Protective Clothing for Proximity Fire Fighting. In addition, different key variables were examined for each type of test to show the effects of exposure temperature, moisture, and pressure in the case of conductive heat resistance, and radiative heat flux for radiant heat resistance testing. The study demonstrated that different test methods rank materials systems differently and that no one test can be used to predict performance in all fire ground situations. The effects of specific variables for some tests indicated a range of performance for the different material systems evaluated. For example, conductive heat resistance showed varying effects for moisture in clothing systems—sometimes augmenting performance, in other cases diminishing protection times. The study offers a number of recommendations for further development of test methods and performance criteria which can be applied to fire fighter protective clothing.