What is a good air permeability value for a glazed unit?

Air permeability measures a glazed unit’s ability to prevent air passing through. It is measured on a scale of class 1 to class 4 with class 4 being the highest level of prevention. Testing a glazed unit for air permeability is an essential part of understanding a glazed unit’s insulating, weather resistance, and heat retention performance. Current regulations require that new window installations must achieve at least a class 1 or class 2 score depending on the climatic zone where the building is located.

Exlabesa glazed units air permeability capacity

At Exlabesa, all our products are tested to the most rigorous industry standards to ensure that they provide the best protection possible. With regards to air permeability, all our windows are tested to wind speed pressure conditions up to 600Pa. They achieve extremely high ratings, between class 3 and class 4 depending on the specifications, and meet all standards set out by BS6375-1.

Have a look at this comparison table for an overview of our different products’ performance capacity:


Air permeability (Pa)

Watertightness (Pa)

Wind load (Pa)

U values (W/m²K)

Casement windows (KC51) 600 1050 2000 1.5
Sliding doors (Xlaslide) 300 200 1600 1.5
Tilt & turn windows (KT51) 600 450 2000 1.5
Bifold doors (Xlafold) 600 450 1200 1.5


High performing aluminium glazing

Birds eye view of window profile

At Exlabesa, we have decades of experience manufacturing and supplying high performing aluminium glazing products. Our team of experts continuously ensure that all our products are developed in line with current and predicted future standards. Our aluminium systems have been used in high profile glazing projects around the world and are industry renowned for their superior performance and outstanding aesthetics.

Air permeability is an increasingly important consideration across the glazing industry. As industry standards become more and more stringent, it is essential that all our products are developed and tested to ensure only the best insulation capacity. By using the latest technology including multi-chambered aluminium profiles and polyamide thermal breaks, we can ensure that our windows are of the best possible standard.

If you’d like to find out more about any Exlabesa products, get in touch today. For more information call 01302 762 500 or contact us online.


We will be closed from Wednesday 23rd December and will reopen on Tuesday 2nd January.