By surrounding a 32 oz. Nalgene (or similarly sized bottle) with both a 1/2 in. of closed cell foam and heat-reflecting foil layer, the Aquatherm helps to keep your water from freezing in cold conditions. The same technology can keep drinks nice and cool in the heat of the summer. Two attachment methods make the Aquatherm easy to take along - you can either slip a couple of your packs side compression straps or your hip belt between the Aquatherm’s hook and loop straps. Other features include a draw cord closure (doesn't freeze like zippers can) and a bombproof, 210-denier nylon outer shell and liner.