I've mentioned this before, I used fridge truck (-18°C) insulated panels that I got free from an industrial body builder specialised in Freezer trucks! When an insulated truck tries to get under a bridge that is too low, it wrecks the front, but they have to replace whole panels, leaving a lot of reusable material. The walls are 50mm and the roofs are 80mm. It cost them to have the stuff destroyed! Unfortunately, I don't have any UK contacts for this, but, for large surfaces, (like tractor sheds Andrew!!) it could really be worth while! The attached photo is the North wall of my workshop, with double doors 4m high X 2x2m wide with a "pophole" 2.2m x1m which is my front door! The strap anchors are still in place as the are a real pain to remove. The lower part of the Truck sides are cover with stainless sheet, an added bonus!