Firefighters, by the intrinsic nature of their occupation, are subjected to a barrage of intense radiant and convective heat fluxes, protected merely by a thin composite layer of fabric for thermal insulation. The exertion requisite of firefighting can raise the temperature inside their turnout coat as well, contributing to the possibility of debilitating heat-related injuries. To mitigate the severity and frequency of such injuries without encumbering the firefighter with excess weight, an assembly of shape memory material was designed that would activate under thermal load to create an insulating air gap between insulating layers in the turnout coat. A prototype gear was constructed and tested, the heat transfer within it modeled. The enhanced coat was demonstrated to yield a significant performance benefit over a turnout coat without the expanding assembly.