Drysuits are the preferred exposure suit when diving in cooler waters or when the extended bottom time is desired. They allow divers to extend dive times substantially compared to wearing a wetsuit or semi-drysuit. New designs, materials, technology, and undergarments mean that they are now commonly used in warmer waters (20° Celsius/68° Fahrenheit or more) as well.
As previously stated, wetsuits allow a layer of water to enter, and body heat warms the water. In contrast, drysuits do not allow water to enter. The suit itself provides minimal insulation. The heat is provided by wearing clothing called undergarments. The colder the water, the warmer the garments need to be.
Drysuits use dry zippers to allow a person to put it on and to prevent water from entering. These zippers are similar to those used on an astronaut’s spacesuit. Modern suits use either steel or plastic zips. In order for a drysuit to truly stay dry, every seal must be perfect. Therefore, the suit is fitted with dry seals. Wrist and neck seals are made of latex, neoprene, or silicone.
To compensate for the increase in pressure as the diver descends, air must be added to the suit to prevent it from squeezing the diver. Suit squeeze is extremely uncomfortable because of the lack of air inside the suit makes it cling to the diver’s body. Drysuits have an inflator valve (much like those found on a BCD) on the front of the suit, which allows the addition of air. A low-pressure hose, fed from the first stage on the cylinder, allows the diver to add gas to relieve the squeeze. On ascent, the gas in the suit will expand. Therefore, the suit has a dump valve, which allows the expanding gas to be released, enabling a safe controlled ascent.
Using a drysuit is quite simple but does require specific training. This training can be combined with most training programs, including Open Water 20, or as a separate specialty program.