In reply to kingborris:
> The PHD website was my first port of call before posting here, but I couldn't find the info I'm after.
> ??????The lack of this info makes comparing different jackets very difficult Would a jacket with 150grm 800FP down be warmer than one with 180grm of 700FP? Who knows!? It'll be thinner and lighter for sure but the warmth is a mystery.
If it's thinner it won't be warmer - higher fill power means you need less weight of down to create the same volume of jacket; there will be *slightly* more air to down ratio but not enough to make a significant difference, total volume of air trapped will be pretty similar in two jackets that look identical size when puffed up. The higher fill power will just pack down a little bit better.
If we wanted a way to compare jackets across brands for warmth, an industry standard volume rating would be useful - but even then fit and features (such as integrated hood, high neckline/low bum line, baffle type etc.) make such a difference to heat loss in the real world that it would be of limited value compared to putting on a jacket and feeling for yourself.