Water Vapour Transmission Rate WVTR
topic
WVTR tests seal fabric specimens over a desiccant-filled or water-filled cup and measure mass change rate under defined temperature and humidity differentials, expressing breathability as grams of water vapour transmitted per square metre per 24 hours; the inverted cup method better represents outward vapour diffusion from body perspiration.
Role
Quantifies the breathability of waterproof-breathable membranes, coated fabrics, and medical barrier materials, providing the evaporative resistance data required for comfort prediction models and certification of protective garment systems.