Catching the winter cold

With winter drawing closer it's time to do some DIY again. Thing is, I'd like to insulate the hives over winter by wrapping them up (not literally, in whatever way you want to use that word now) in celotex. Although no bee book I have looked into so far recommends it, I read a newsletter in one of the beekeeping magazines I now receive which told of positive experiences with insulating the hives in winter. This makes sense to me. Most of the time the bees die because, although they have sufficient food, it is too cold for them to break cluster. So, if they're insulated, they can; besides, they should not need as much food, as they do not need as much energy to keep themselves warm.
With apparently so many advantages it is strange that not more beekeepers are celotexing their hives. I hope I don't find out why not in spring...
Luckily the school - a Victorian mansion that needs constant loving attention from our handymen - has scraps of celotex. So I nabbed these and cut them to size.

When to put them on the hives? I have no clue, but anytime now. As it's half term I'll do this without the pupils, but my niece is coming, so I'll wait for her. I'm sure she'll be excited to help and then see photos of herself on the web.