Extraflex Polyester 3 Mil Roof Felt Underlay

About this product

Viapol Extraflex Polyester is an SBS polymer-modified bitumen waterproofing membrane on a polyester carrier, supplied here as the 3 mil underlay grade. It is intended as the waterproofing layer in a modern roof build-up in harsh weather.

The polyester reinforcement is what gives it its movement capacity: it stays flexible at -15°C and will stretch to 2000% elongation before it lets go, so it takes structural movement without cracking. It also holds up well against thermal shock and ageing.

The finished membrane wants protecting, either with a mineral or slate-faced cap sheet, paving, ballast or a suitable protective coating depending on the top finish chosen. Top finishes available are mineral (white, grey, red or green), polypropylene or sand, with a polyethylene or polypropylene underside.