Glidevale Protect A1 roof tile underlay can be used for all pitched roof constructions (tiled and slated), whether the insulation is at ceiling joist level or at rafter level. It is a twin-ply construction of polypropylene non-woven spunbond layer and PP film. Glidevale Protect A1 is a ‘third-generation’ roofing underlay which has been developed specifically to overcome the disadvantages of traditional Type 1F felts and second generation plastic sheet materials.