The use of ETFE foil is becoming more common as a component of cladding systems. ETFE cushions provide a lightweight, cost effective and geometrically flexible solution with good thermal performance and high transparency. They are typically installed within special aluminium boundary profiles, which are in turn supported by steel, timber or bi-directional cable nets.

Foil thickness between 50 and 250 microns are usually employed in 2 or 3-layer cushion construction with a constantly maintained air pressure between 200 and 750 Pa. This pressure may be automatically increased to support higher snow loads.

Because of the high strain characteristics of ETFE foil it is possible to install a flat unstressed membrane into a planar boundary frame and develop the rise of the cushion to approximately 10% of its span solely through elastic strain of the material under inflation. This no longer works satisfactorily when a higher cushion rise is required to reduce stresses under load, or when the boundary frame is curved or warped.

Tensys have developed unique software for the patterning of ETFE foil cushions. This permits the development of wrinkle free surfaces, even when inflated within highly non-planar boundary frames.

Under load analysis the variation of pressure within the cushion must also be considered, especially for load cases with a combination of wind pressures and suctions. The inTENS software has options to specify constant pressure, constant volume or constant mass of air within a closed cell during its 3D finite element analysis.