sd: diffusion-equivalent air layer thickness [m] V (=WDD): water vapour transmission rate
| sd [m] | water vapour transmission rate V [g/m²d] | ISO 7783-2 |
| < 0.14 | > 150 | I (high) |
| 0.14 - 1.4 | 15 - 150 | II (medium) |
| > 1.4 | < 15 | III (low) |
low sd-value = high water vapour permeability
Liquid water transmission rate
W: water absorption [kg/m²]
w: water absorption coefficient [kg/m²h0,5]
t: absorption time [h]
| w [kg/m²h0.5] | ISO 1062-3 |
| > 0.5 | I (high) |
| 0.1 - 0.5 | II (medium) |
| < 0.1 | III (low) |
low w-value = low capillary water absorption
ideal: sd < 0.14 m, w < 0.1 kg/m²h0.5
