Dry suits are generally used where the water temperature is between −2 and 15 °C (28 and 59 °F). Water is prevented from entering the suit by seals at the neck and wrists and the opening for getting the suit on and off is typically closed by a waterproof zipper. The suit insulates the wearer by maintaining an insulating layer of air in the undersuit between the body and the suit shell, (in exactly the way that thermal insulation garments work above water) or by using a watertight expanded neoprene suit shell, which is inherently insulating in the same way as a wet suit, and which can usually be worn with additional insulating undergarments.[22][23][24]