Why is windtight construction important?
Insulation effect of stationary air
Unprotected insulation material: Air movements in the porous structure make the insulation less effective.
Protected thermal insulation
Protected insulation material: No air movements are possible in the porous structure, full insulation effect.
An example: The thermal insulation effect of a woollen jumper is based on the stationary air inclusions in the fibres: as soon as a cold wind starts to blow, the insulation becomes less effective. However, the insulation effect is restored if you wear a thin wind-breaker, which itself has no significant heating function, over the jumper.