Rab’s Infinity sleeping bags are extremely warm for the weight as they are filled with 850 fill power down and have an ultralight shell made of Pertex Quantum GL plus a complex construction that allows the down to loft efficiently. The bags are beautifully soft and comfortable and pack away really small. I’ve used the Infinity 500, which weighs 871 grams, for winter camping in the Cairngorms and I took the Infinity 300, which weighs 656 grams, on the Scottish Watershed. The latest versions of the Infinity, which I haven’t used, should be even better as they are filled with water-resistant down.