Can anyone explain to me the difference between breather paper and membrane - or are they the same thing? I'm using Klober permo forte for underlay on my pitched roof, and I had assumed that the breather membrane I would use on my dormer walls (cladding, 25x38 batten, breather membrane, 18mm ply, studs/insulation,vapour barrier, plaster board - outside to inside) could be this? But is this an expensive option - should I use klober permo frame, or something else. So, fundamentally, is breather paper used on timber walls different - does a different job - than breather membranes under tiles? I appreciate the latter stops water ingres, allows vapour egress - does breather paper do this? any help appreciated!!