Although Knauf Insulation DriTherm 32 and DriTherm 37 cavity slabs are water-resistant (thanks to their water repellent additive), this does not mean that they are waterproof. Whilst the slabs are able to resist the penetration of water to a certain degree, they are not completely impenetrable.Both the DriTherm cavity slab 32 and DriTherm cavity slab 37 have a water vapour resistivity of 5.00MNs/g.m. Earthwool slabs are non-hygroscopic and are therefore approved to use in all exposure zones, as they will not absorb moisture. Another welcome benefit of the water-resistant binder used in Knauf slabs is that it eliminates the chance of rot, vermin, or fungus.For this reason, we highly recommend Knauf slabs for people who live in high-rainfall areas. People choose Knauf Earthwool slabs when they need full-fill insulation that has a long lifespan. The nature of full-fill insulation slabs further ensures that they do not sag or droop over time - promising maximum protection for the lifetime of your build.