FEP allows 97% of UVA and UVB light to pass through it. Laser light will pass through FEP without any deviation. So the choice of the containing material was clear. The challenge was to create a defined space which could encapsulate a given volume of air. In this case a cube with 1m sides was chosen. The encapsulating material had to be as light as possible so 25 micron thick FEP was used by Holscot. Using a variety of their own proprietary welding techniques, Holscot welded 1150mm wide sheets together to form a 1m cube. Because of the flexible nature of the FEP film, it was supported all round by a metal scaffolding. The whole assembly had to be transported intact to Leatherhead with a police escort.