The Sioux UL 100 is the lightest bag tested at a very low 600 grams. It also packs very small even without its compression stuff sack, making it ideal for ultralight backpacking in hot climates. For UK summers it’s pushing the limits even for warm sleepers as it’s very thin. I was just comfortable at 14°C but would probably need warm clothing at lower temperatures. The bag is roomy enough to wear thick clothing inside. It has a well-fi tting hood and a baffl e behind the zip; the latter runs smoothly. There’s a second drawcord just inside the bag that pulls the bag round the shoulders without the hood needing to be closed. The seams are sewn-through, but this doesn’t really make a difference in a bag this thin. The lining is only attached round the edges of the bag, which will help keep warm air in. If weight is crucial and you want a synthetic fill bag then this is one of the lightest around. A bag like the Lynx weighing a couple of hundred grams more is much, much warmer though.