Sierra Designs' Flex™ sleeping bags offer a revolutionary new concept in outdoor living: a comfortable night's sleep in the outdoors. The trick is in the Flex™ construction: the bag expands where you need it to, so you can turn and move like you do at home, all the while maintaining thermal efficiency (you stay warm). Our NightCap Hood™ allows side and belly sleepers (75% of us) to keep elbows and arms inside the bag, in their natural position, all night long. Don't take our word for it: get inside a Flex™ bag and try it out. Sleeping on the ground will never be the same.