Air permeability is the amount of air which, due to the test pressure, crosses the tested window in a closed and locked position. The basic permeability is Class 1 at an air pressure of 150 Pa.
The maximum performance is Class 4 (with test pressure over 600 Pa), this level being obtained by the IzoSense window.
If we convert the pressure measured in pascal (Pa) in speed measured in km/h, 600 Pa means 112.5 km/h. This wind speed occurs during the 10-11 level storms when trees are unrooted and the sea waves exceed 12 meters in height.
The windows in Class 4 air permeability have increased resistance to external pressure and provide excellent insulation.