Much more comfortable than foam - Therm-a-Rest NeoAir XLite Sleeping Pad - Past Season

Just as light as ccf (closed cell foam) but much more comfortable. The pad packs down nicely and thus can be stored in your pack. It takes some time to inflate, and you can get a little dizzy at altitude if you try to inflate too fast. Note: I've returned a couple of these (from various stores) due to leaks. TEST YOUR PAD before your trip. The leak repair kit works well.