Wide-mouth Nalgene water bottle. Made out of Lexan plastic. Very tough. Solid screw top lid. Makes and excellent water bottle during the day and hot water bottle at night. Also makes a great Pee Bottle. We recommend a minimum of two per person (one as water bottle, one as P bottle) IF YOU ARE ALSO BRINGING A THERMOS. If you aren't bringing a Thermos/insulated flask you should have two Nalgene bottes for water and a third for your Pee bottle.