Dry Test Thermal resistance

Measuring Plate Area m²

Plate Temperature °C

Air Temperature °C

Dry Heating Power W

Bare Plate Correction W

Wet Test Evaporative resistance

Saturated Vapour Pressure at Plate Pa

Air Vapour Pressure Pa

Wet Heating Power W

Bare Plate Correction W

Ret Limit for Comparison m²Pa/W

Evaporative Resistance Ret

— m²Pa/W

Lower is more breathable

Thermal & Comfort

Thermal Resistance Rct: — m²K/W
Moisture Permeability Index: —
Thermal Resistance: — tog
Thermal Resistance: — clo
Margin Inside Ret Limit: — m²Pa/W

Bare plate corrections are not optional — without them the boundary air layer is counted as part of the fabric and both resistances come out too high. The permeability index runs from 0 (impermeable) to 1 (behaves like the bare plate); values above about 0.6 usually indicate a measurement problem rather than an exceptional fabric.

Sweating Guarded Hotplate Ret, Rct & Permeability Index — free, with the formula and a worked example, at Textile School.