This is a Blizzard Bag. It's waterproof, windproof, reusable and it's also insulating ... in fact independent tests reveal it to have greater insulating properties weight for weight than down!
Obviously the bag would be ideal for emergency situations, just the thing to have stashed in your pack for those 'what if' moments but I think it may well have a greater role. It weighs 385g and is waterproof (can you see what I'm getting at?) that's 385g for a combined sleeping bag / bivvy bag. I'm sure you're thinking, okay but is it really warm enough? The answer at the moment is, I don't know but I certainly intend to find out ... I'll report back with a full review after it's had a thorough testing.