This is a very good question, as too often I see people using Earthwool for insulation in conversion…

I did too once.. Then realised that all the condensation that form when there are two different temperature between inside and outside was getting absorbed by the Earthwool (that’s supposed to be non-hygroscopic) and that could promote rust. Leave it long enough in water and you will understand. I since stopped using it.

These day there are much more suitable materials especially for vehicle that have very thin walls and prone to condensation..

I use and definitely recommend XPS foam.. It does not absorb water and is very clean, light and easy to work with. It comes in sheet of different thickness and colours and it doesn’t go brittle in time like polystyrene..