Aerial 330

Well, “freely” overstates the benefits. It takes a slight effort when you turn to keep the uninsulated bottom of the bag pressed against the pad when you turn. I love the false back design — especially the part about having a -7C sleeping bag that only weighs 450g (!) — but there is a little bit of learning curve to turning without exposing your back side to the cold. There are no drafts, which is nice, but warmth is still prone to escape until you master that skill. Zenbivy’s system is designed to fix such problems: you can turn easily draft-free. I don’t like ZB though because of the extra weight and complication of adding a sheet. A wide quilt is simpler, easier to get in and out of, and mostly solves the draft problem. Also, maybe it’s me, but I’m not going into the backcountry to mimic sleeping in a bed at home.

The Aerial is not a quilt though. It's an absolute minimalist sleeping bag, quite narrow, but has an unfilled backside.

Take a look at cumulus bags. They can do custom fill (up or down, “waterproof” different fabrics etc ) and custom sizing for it as well if you wish. Not cheap but personally I think they’re the best down bags on the market.