Another expensive but excellent option: cashmere. Not something I've seen advertised in bedding, but in clothing there's nothing warmer and lighter that I've found--well okay silk might compare but it doesn't have the cosiness and loft of cashmere. For bedding I supposed I'd have to knit or weave my own, but maybe it is available in high end stores I'd never think to visit. I did see a cashmere travel set advertised, but the blanket was very small. They didn't specify the price, which told me something.

But hey If it's good enough to keep the tummies of Himalyan goats warm in winter, it's good enough for me. I'm told it's combed from their bellies so only the hair they've shed is used, thus they don't succumb to the cold in their service to humanity. Cashmere is very lightweight, lighter per warmth than regular wool as far as I can tell. Just only one thin layer does as much warming as a regular wool sweater or a very thick cottone sweater, and without holding moisture (cotton's fatal flaw in the cold). Keep in mind, my comparison is completely subjective based on what layers I need at certain temperatures to keep warm during dog walks. If I could afford cashmere longjohns I'd have 'em; until I saw this thread I never thought of cashmere for blankets but why not?! In my real world, microfibre is a great substitute both on the bed and in longjohns. One clear flaw of cashmere besides price is the weakness of the fibre, hence the constant appearance of holes, darn it.