Before xmas we bought a new (cheapo) duvet, as it was cheaper to replace the old one than the cost of getting it cleaned. Anyway, right out of the bag the new duvet didn't appear as good as the old one. They were both rated at 13.5 TOF, but the new one was obviously thinner. It wasn't as warm either (even taking the colder weather into account) and we needed an extra blanket on top. Fast forward to this week and we got another cheapo duvet - this time from Sainsburys, which again is rated at 13.5 TOG and is much better then the last one we bought (compares well to the original one). So purely out of interest, I'd like to test if the TOG rating of the various duvets measures up - has anyone else tried this?
From a DIY perspective, I'm planning on measuring the temp. under the duvet, while warming the bed with an electric blanket (and having the room temperature more-or-less constant). The idea is that the greater the thermal insulation, the higher the under-duvet temperature will be. The tricky bit will e converting this temperature to a heat- loss figure and then to a thermal resistance figure. Any pointers on how to do the sums would be appreciated.