I've heard of a few units offered that are essentially a ground cloth sans insulation with the sides and top fully filled. Outdoor gear is oftentimes just as much slave to fashion and tradition as clothing. There are always a few potential tradeoffs in overal useability. All I know is, I once rolled down a slight incline in the desert while asleep and woke up with the bottom of the bag now on the top. So I stick with a traditional mummy.