I love my Sea to Summit Trek TKII. It is a down bag, the down is treated to be some what water resistant. It is not a mummy bag and it is not a rectangle bag, but it is a little of both. I really like the extra room the Trek line of sleeping bag offer. If you have a couple of the Trek bags they can be zip together to make one large bag for 2 which is really nice when the wife comes a long. Comes with a storage bag (never store a sleeping bag in a stuff bag/ compression bag), a bag for washing the sleeping bag and a compression bag. Mine is a large and it weighs about 2 lbs and 2 oz. Compress down to be smaller than a 2 liter bottle.