Breathable FeltBreathable underlay roofing felt 140g sold in 50m rolls at 1.5-metre high bulk saver discounts available This roof membrane is breathable. It allows the flow of air through but remains waterproof. It can be installed on timber joists or panelled roofs with slate or traditional tiles. This membrane helps avoid problems caused in winter by condensation that forms inside the roof. The weight of this felt is 140 grams so it may need to be tapped if you live further north to confo..