I have been watching selly telly again and am tempted by Nasa (apparently) developed silver material which fits behind radiators. They have a natty little fititng, two prongy things which just hang it behind, rather than one having to use masking tape which I remember seeing in the past. My house is pretty well insulate, cavity wall new windows etc. What do you think? Is it only worth it for outside walls, or not worth it at all?