I have a 2# Rab 20* mummy bag that I hardly ever use because it doesn't leave me any room to roll around, I can't even fit an extra layer on inside of it if I wanted to extend the temp rating a little lower. My wife loves it and she takes it if she's going somewhere without me. If we're going somewhere together we have a 2 person bag from Big Agnes that is the best thing ever! There's room to get comfortable and it's incredibly flexible in its comfort range. We were looking for a lighter option and just picked up a Feather Friends Flicker which we hope to be able to use as a 2 person quilt but it also has the ability to zip up to be a one person hoodless mummy bag that's rated to 20*. The Feathered Friends bag packs to about 8 liters in size. As someone has mentioned, the other half of the system is the pad, my wife and I both use the Thermarest NeoAir X-therm. We sleep on the snow a fair amount and in the high alpine and these pads have been great. I've seen one get sliced on sharp granite shards so some care is necessary but the comfort and insulation is great for the weight and packed size.