Comprising two skins of steel (or aluminium) with insulation sandwiched between, this roofing and cladding system has been the market leader since the mid 1980s. The key to its popularity being its versatility and cost effectiveness.

The most commonly used combination of materials has, for some time now, been : plastisol coated galvanised steel top sheet (available 20 different colours), glass fibre insulation of requisite thickness to satisfy the specification, Ashgrid spacer bar system, and white galvanised steel lining panels. Thus providing an insulated weather-tight roof, with an aesthetically pleasing appearance both internally and externally.