Firefighting personal protective equipment (PPE) has evolved through significant technological improvements over the past half century. Enhanced thermal protection from modern PPE and the introduction of self-contained breathing apparatus (SCBA) has enabled firefighters to work longer and more efficiently in immediately dangerous to life or health environments. Despite these advancements, performance limitations remain in many parts of the turnout gear ensemble. In particular, the SCBA mask represents a critical potential failure point, as a compromised lens can result in loss of vision, facial and airway burns, and other injuries associated with the inhalation of products of combustion. It has been speculated that repeated exposures to mild to moderate thermal exposures may cause a change in the mechanical properties of the SCBA face piece lens material, potentially weakening the mask and precipitating a catastrophic failure of the lens. To address this concern, a new laboratory instrument has been constructed to provide repeatable cyclic thermal exposure for SCBA facepieces building on the existing NIST radiant panel apparatus that has recently been adopted by the NFPA 1981 standard. SCBA facepieces that were worn in the field were also harvested to allow important comparison with changes caused by typical fire service use conditions. With this automated system SCBA facepieces were exposed to 1 kW/m 2 , 2 kW/m 2 and 5 kW/m 2 radiant heat flux exposures (NIST Thermal Classes I, II and III, respectively) for one, 10 and 100 cycles. Repeated exposure to Class I and II heat fluxes do not have a significant effect on thermal damage or mechanical properties compared to unexposed samples. While a single exposure to the 5 kW/m 2 condition also resulted in no visible thermal damage or mechanical changes, microcracking was consistently observed by 10 cycles and continued to extend in the 100 cycle samples. Though visible damage was evident after 10 cycles, mechanical properties were not affected. On the other hand, substantial reductions in ductility were noted after 100 cycles, with changes in mechanical properties that were similar to those measured in the field worn samples. In field worn samples where significant reductions in quasi-static tensile properties are noted, significant reduction in dynamic energy absorption were also measured. The 5 kW/m 2 -100 cycle samples that resulted in the most significantly reduced ductility were harvested from the area where visible surface microcracking was present. However, samples from the edges of the exposed area, where no visible damage was noted, also demonstrated smaller but significant reduction in ductility. Thus, there does not appear to be a one-to-one correlation between visual indications of thermal damage and reduced mechanical properties. However, if an SCBA facepiece shows visual indications of thermal damage or has been repeatedly exposed to Class III environments, the unit should be closely inspected and replacement considered.