I ain't no expert, but the most common insulation seems to be a aluminium backed polyurethane insulation. celotex, exotherm are two that i know, available from builders merchants. available in different thicknesses and usually in 8 x 4 size sheeting. I managed to get some slightly damaged sheets for my SWB for £20, enough to do the whole van. Hope this helps :ILU:
Hi for all of the campervan conversions that i carry out i use Double Foil Single Bubble Thermal Insulation. I find this to be a very good insulator as it keeps the van warm in the winter and cool in the summertime. It is lightweight and easy to work with and it is water and vapour resistant. I hope that this helps.