I'm doing the Welsh 3000s in a few weeks so I'm trying to get my kit down to be as small and light as I can without sacrificing safety. Currently I carry a traditional large, orange, polythene Bivvy bag and a paper-lined foil blanket. Together they weigh about 1.3kg and are VERY large. They are each slightly larger than A4 and, together, about 35mm thick.
This thermal survival bag should be able to replace them both. I ordered on a Friday and EVAQ8 had it here by Tuesday. It is about half a jotter pad in area (A7?), about 12mm thick and weighs 225g so I'm barely going to notice it in my Day sack. It says I should keep it in the vac-pac until required so I can't comment on the quality etc (Hopefully I will never find out) but I'm chuffed to have cut so much bulk and weight from my kit.