Thermarest NeoAir XTherm
This is a fantastic mat if you want lightweight, small packed size, and WARM. It packs into the size of a 1L water bottle yet has an R-value of 5.7 - enough for winter camping - and is comfortable to boot. Reflective baffling inside the mattress creates pockets of air that trap heat and keep the mat stable. You can inflate it by mouth; however to keep moisture to a minimum inside it's a good idea to purchase a Pump Sack, Torrent Pump or Mini Pump. Comes with stuff sack and repair kit.
Regular Large R-value 5.7 5.7 Weight 430g 570g Width 51cm 63cm Length 183cm 196cm Thickness 6.3cm 6.3cm Packed dimensions 23 x 10cm 28 x 11cm