Curve, Mummy, Egg, and Brick is simply a description of the shape of the sleeping bag. The different models are to accommodate different shapes and sizes to give the best possible performance needed. Curve A sleeping bag with a snug fit slimming in at the waist and feet but broader at the shoulders and hips. Mummy A sleeping bag with a somewhat tight fit. Broad at the shoulders but slimming in all the way to the feet. This may vary depending on the individual sleeping bag. Egg The Egg (comfort) fit has a lot of the advantages of the curve and mummy but gives a bit of extra space in comparison. It’s normally thicker/more insulated to achieve the same temperature. Brick A sleeping bag with a rectangular fit, a lot of space and can be zipped all the way up to be used as a duvet or blanket. Offers great comfort but a poorer performance overall.