Moisture Barrier Breathability and Physiological Performance
topic
Moisture barrier breathability measured as water vapour resistance Ret by ISO 11092 sweating hotplate method determines how effectively evaporative cooling from sweat can reduce firefighter core temperature during high-metabolic-rate firefighting, with Ret below 20 square metres per pascal per watt providing meaningful breathability and values above 30 significantly impairing evaporative cooling, creating the fundamental tension with waterproofness where higher breathability increases heat stress protection but may reduce water and steam barrier performance.
Role
Quantifies the physiological heat stress burden from moisture barrier resistance to sweat evaporation that determines whether firefighters can sustain the high work rates of structural firefighting without dangerous core temperature elevation, with breathability being the primary clothing property governing safe working time under heat stress conditions and the performance parameter whose improvement through moisture barrier material development provides the greatest physiological benefit for operational firefighting sustainability.
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