FIBRANskin SMART | Breathable vapour control membrane

FIBRANskin SMART is an intelligent vapour control membrane manufactured in accordance with EN 13984:2013. It is neither a vapour barrier nor a breathable membrane: its diffusion resistance varies according to humidity conditions, with a nominal Sd value of 13 m and a range of 8–18 m in accordance with EN 1931 (23-0/75). It is installed on the warm side, beneath the thermal insulation, where it acts as a retarder of outgoing water vapour diffusion in winter and as a regulator of smooth diffusion towards the interior in summer. It offers the highest tensile strengths in the FIBRANskin range — 390 N/50 mm (MD) and 380 N/50 mm (XD) — joint strength of 280 N/5 cm and documented alkali resistance. Waterproofing class W1, Euroclass E, mass 92 g/m², thickness 0.2 mm, roll 1.50 × 50 m (75 m²). Suitable for areas with low to medium humidity. 10-year guarantee.

The ARGYNET View

What ‘smart’ means — and why it’s not just marketing.

A standard vapour barrier has a fixed Sd value. This solves the winter problem (it stops water vapour before it enters the insulation) but creates a summer problem: if any moisture becomes trapped inside the insulation — from a leak, construction moisture or a poor seal — there is no way for it to escape. The vapour barrier keeps it in, winter and summer alike.

SMART varies its resistance from 8 to 18 m depending on the relative humidity in its environment:

Winter — dry indoor air; the membrane ‘closes’ towards high Sd values and acts as a barrier.

Summer — high humidity; the membrane ‘opens’ towards low Sd values and allows trapped moisture to dry out towards the interior.

It is a fault-tolerance mechanism: it gives the structure a second chance to dry out. In timber roofs, where trapped moisture leads to rotting rafters, this is of real value.