Have you ever looked inside a cavity wall? You will often see hundreds of droplets of water beading on the inside of the outer wall. This is usually condensation as the inner walls breathe and damp accumulates on the colder outer brick work. The void in between is sufficiently ventilated to allow the condensation to escape as conditions improve.
So, why isn't outdoor clothing constructed in the same way? Well, some of it is. The FurTech jackets have a two layered construction with a furry "void" in between. This keeps the outer "wall" from touching the inner one.