Evaporative Resistance Ret Measurement ISO 11092
topic
Evaporative resistance measurement on the sweating guarded hotplate uses the same instrument as thermal resistance testing but operates with the plate surface supplied with water at skin temperature, creating a water vapour pressure gradient through the specimen to a drier ambient environment, with the resistance calculated from the steady-state evaporation power and the vapour pressure difference. The test distinguishes fabrics by their resistance to moisture vapour diffusion — microporous membranes permitting vapour passage through interconnected pores while blocking liquid water droplets, hydrophilic membranes transmitting vapour by absorption-diffusion-desorption through the polymer matrix, and untreated fabrics transmitting vapour freely through fabric interstices. Results in square metre pascal per watt classify fabrics from highly breathable through to vapour-impermeable.
Role
Ret measurement is the internationally standardised evaporative resistance method that underpins all breathability classifications in protective clothing standards — providing the single quantitative parameter that determines compliance with EN 343 rain protective clothing breathability classes and EN 469 firefighter garment physiological performance requirements, making Ret the most commercially and regulatorily consequential breathability measurement in the global performance textile industry.