A dry suit or drysuit provides thermal insulation or passive thermal protection to the wearer while immersed in water, and is worn by divers, boaters, water sports enthusiasts, and others who work or play in or near cold water. The drysuit protects the whole human body, except the head, hands, and possibly the feet. Drysuits are used typically in these cases:

• where the water temperature is below 15°C (60°F).
• for extended immersion in water above 15°C (60°F), where discomfort would be experienced by a wetsuit user.
• with an integral helmet, boots, and gloves for personal protection when working in and around hazardous liquids.

The main difference between drysuits and wetsuits is that drysuits are designed to prevent water entering. This generally allows better insulation in drysuits making them more suitable for use in cold water. Drysuits can be uncomfortably hot in warm or hot air. They are generally more expensive than wetsuits.

Parts of a dry suit

Needed

Shell

The main part of the drysuit is a waterproof shell made from a membrane type material: neoprene, foam rubber, or a hybrid of both.

Membrane

Membrane drysuits are made from thin materials, and thus by themselves have little thermal insulation. They are commonly made of vulcanized rubber, or laminated layers of nylon and butyl rubber. Membrane drysuits typically do not stretch, so they need to be made oversized and baggy to allow flexibility at the joints through the wearer's range of motion. This makes membrane drysuits easy to put on and get off, provides a great range of motion for the wearer, and makes them comfortable to wear for long periods, as the wearer does not have to pull against rubber elasticity.

To stay warm in a membrane suit, the wearer must wear an insulating undersuit, today typically made with polyester or other synthetic fiber batting. Polyester and other synthetics are preferred over natural materials, since synthetic materials have better insulating properties when damp or wet from sweat, seepage, or a leak.

Reasonable care must be taken not to hole or tear membrane drysuits, because buoyancy and insulation depend completely on the gas pockets in the undersuit. The drysuit material offers essentially no buoyancy or insulation itself, so if the drysuit leaks or is torn, water can soak the undersuit, with a corresponding loss of buoyancy and insulation.

In warmer waters, some wearers wear specially designed membrane drysuits without an undersuit. These are different in design, materials, and construction from drysuits made for cold water diving.

Membrane drysuits may also be made of a waterproof and breathable material to enable comfortable wear when out of the water for long periods of time. Sailors and boaters who intend to stay out of the water prefer this type of suit.

Neoprene

Neoprene is a closed cell foam synthetic rubber, containing millions of tiny air bubbles, forming a buoyant and thermally insulating material. If torn or punctured, a neoprene suit still keeps the insulation and buoyancy of the neoprene's bubbles when flooded. Being made of a fairly rigid dense material, they are not as easy to get on and off as membrane drysuits, and their buoyancy and thermal protection decreases with depth as the air bubbles in the neoprene are compressed, like with wetsuits. Neoprene also tends to shrink over the years as it outgases and slowly becomes more rigid. An alternative is crushed or rolled neoprene, which is less susceptible to volume changes when under pressure and shrinks less. With neoprene suits thermal under suits are usually worn, however, less insulation is needed thus reducing the amount of weight needed to counteract its buoyancy than a membrane suit which uses a thicker undersuit.

Hybrid

Hybrid suits combine the features of both types, with a membrane top attached to a neoprene bottom near the waist. The neoprene part is usually configured as a sleeveless "farmer-john" that covers the torso as well. This style is often used for surface water sports, especially in very cold water. The tight fitting lower part lets the wearer kick while swimming, and the loose fitting top allows easy arm movement. The torso covering also provides additional self-rescue or survival time if the suit leaks.

Seals

Seals at the wrists and neck prevent water entering the suit by compressing in a ring like a rubber band around the wrists and neck. The seals are not absolutely watertight, however, and the wearer may experience some seepage during use. The wearer will also get damp due to sweat and condensation. The seals are made from latex rubber or neoprene. Latex seals are supple but easily damaged and deteriorate with exposure to oils, oxygen, and other materials, so they must be replaced periodically, every two years or more. Neoprene seals last longer, but, being stiffer, let more water enter because they do not seal as effectively as latex seals to the contours of wrist and neck skin. They are also typically glued and sewn together to form a ring, and may leak along that seam.

Waterproof entry

Modern dry suits have a waterproof zipper for entry and exit which was originally developed by NASA to hold air inside astronaut space suits. The zipper is commonly installed across the back of the shoulders, but can also be found diagonally across the front of the torso, on the side, or straight down the middle of the front or back.

There are many zipper arrangements in use because the zipper is very rigid, and cannot stretch at all, which can make it difficult for a user to get into and out of the suit. The zipper opening is often quite small, since a large zipper makes the suit stiffer and more difficult to use. Some complex zipper arrangements that wrap around the neck or chest let the suit swing open with a flap or hinge point.

Dry suits may also be fitted with an extra waterproof zipper "fly" to let the user urinate when the suit is worn for long periods. Some snug-fitting suits may also use wrap-around expansion zippers that allow the suit to expand or contract to fit different size people.

Before waterproof zips were invented, other methods had to be devised, with the most common being a long rubber entry tunnel which would be flattened shut, then rolled together from the sides and finally folded and clamped with a metal clip. An early example was the Sladen suit, where the entry tunnel was at the umbilicus. The Louisiana-based drysuit company Aquala still makes a "historical" diving suit of that kind.

Another type was a rubber tunnel that protruded through a normal cloth zipper. The tunnel would be rolled shut and the zipper closed to hold the roll in place. At least one make of old-type British frogman's drysuit was one-piece with a wide neck hole for entry; the bottom of the hood and the edge of the suit's neck hole were held together by a large circular steel clamp around the neck; there was a watertight seal in the bottom of the hood. Two-piece drysuit designs in full length for year-round use and "shorty" styles for summer-season use were also common in the 1950s and early 1960s. Two-piece suits of the period include the American-made Spearfisherman frogman suit, U.S. Divers Seal Suit and the So Lo Marx Skooba Totes suit, the Italian-made Pirelli suit and the UK-made Heinke Delta suit and Siebe-Heinke Dip suit. These suits were sealed at the waist by rolling together the excess material at the bottom of the shirt and the top of the pants. A cummerbund, rail, or surgical tubing was sometimes provided to make the seal more waterproof. A modern version of the two-piece drysuit is manufactured by Customworks of Idaho. Though lacking such features as valves and zippers, these suits still have certain advantages over their modern counterparts. For example, they are cheaper, less bulky, more easily repaired and the footed pants could also double as fishing waders.

Optional

Thermal undersuits

For cold-water use, especially diving under ice sheets, the user will usually wear a thick undersuit in a membrane dry suit. The thickness of undersuits varies and can be chosen by the wearer according the water temperature. Thinsulate is the preferred fabric for undersuits. More recently, aerogel material is being added to conventional undergarments to increase the insulating properties of those garments. Neoprene dry suits are made from a foam-rubber sheet containing tiny air bubbles, which provide insulation by themselves and generally eliminates the need for an undersuit. A neoprene wetsuit can also be worn under a membrane dry suit for extra protection against condensation and leaks.

Gloves, mitts, and 3-finger mitts

Drysuits may have wrist seals, permanently attached gloves/mitts, or a third option known as the attachment ring (described below).

If it is not important to have exposed bare hands, permanently attached heavy rubber gloves or mitts can help make getting in and out of the suit much easier since there is no need for the suit to tightly seal around the wrists. Instead, the wearer can slip into the attached gloves as if they were a loose-fitting coat sleeve.

Full-hand diving mitts can be sometimes useful in extreme environments such as ice diving.

Three-finger mitts are a midpoint between gloves and mittens. In the three-finger mitts, the fingers are arranged like the science-fiction Vulcan salute. This provides slightly better hand-grasping dexterity while still permitting heavy insulation around the hands.

Hoods

The drysuit may also have an integrated hood, which seals water out around the wearer's face, and helps keep the wearer's head warm. The integrated hood is often latex rubber that fits tightly around the head, but can also be made from neoprene or membrane to allow an insulating cap to be worn under the hood. Care must be taken to avoid the hood making a waterproof seal around either of the ears, as this would risk an eardrum bursting outwards at depth.

Separate (non integral) neoprene hoods for use with a dry suit are different from wetsuit hoods, because they cannot be tucked inside the suit at the collar, as this would compromise the neck seal; with these the wearer's head gets wet, which would be a risk when diving in contaminated water.

Helmets

When a diver needs to be underwater for long periods of time day after day, a snug-fitting elastic hood can cause uncomfortable pressure sores on the ears, face, and jaw. To alleviate this and to permit easy communication with the surface and between divers, a hard metal or plastic diving helmet may be worn with the drysuit. This can be separate from the drysuit with its own watertight neck seal, or it can be permanently attached with a neck ring, and air from the helmet can enter into the suit.

Boots

Most commercial diving dry suits have heavy built-in boots. Sport diving suits may have boots or thin sheet-rubber booties. Surface dry suits may have booties or ankle seals to allow better foot control of water skis and surfboards. Surface dry suits may be used with separate non-waterproof neoprene booties for foot warmth, and aqua-shoes for protection while using personal watercraft.

For a commercial environment where the option of interchangeable boots for different sizes of feet is desired, the legs of the dry suit can also be fitted with attachment rings (described below). Some commercial divers order their suits without boots and install rubber work boots such as those used by miners or [[Firefighter|firefighters].

Weight boots

For commercial drysuit divers who must work on the sea bottom or on an underwater platform (such as under an oil rig), the drysuit may be fitted with heavy metal boots to keep the diver firmly weighted down. This allows the suit to be comfortably inflated like a balloon as the diver works, without concern that the diver may float uncontrollably to the surface. These divers cannot swim freely, and may need to ride an underwater cable elevator down to the work area.

Attachment rings

These are typically only seen on professional and commercial diving suits. They allow separate neck seals, gloves, and boots to be joined to the suit with a watertight seal. The attachment ring system uses a support ring inside the suit and a clamping band outside the suit to tightly hold the suit and the separate hood/boot/glove together. They were also used with the neck seals of some old British frogman-type drysuits (see above).

The support ring can optionally be slipped into the sleeve of a regular drysuit that has wrist seals, to temporarily put watertight rubber gloves on the suit, or the wrist seals can be removed and the inner support ring is permanently attached inside the sleeve. The support ring may be a large one-piece unit that can be slipped over the head/hands/feet, or it may be split into halves that can be directly installed up close around the neck/wrists/ankles.

Attachment rings let a commercial diver change his suit to best perform the task at hand. Wrist seals can still be used with an attachment ring suit; they are mounted onto the ring like a pair of gloves.

Valves

A typical diving drysuit has an air exhaust valve, which lets the diver vent gas from the suit during the ascent. This is necessary because when the diver ascends, the air in the suit expands, balloons out the suit, and hinders movement. The air in a ballooned suit can overcome the diver's neutral buoyancy, and can cause a sudden uncontrolled ascent to the surface, resulting in decompression sickness and loss of consciousness.

Vent valves can be automatic, operating as pressure relief valves, or manual, where the diver must raise the valve to vent. Automatic vents are generally at the shoulder, and manual vents are at the wrist. Some older drysuits have no vents, but the diver must lift one of the wrist seals or the neck seal open to vent the drysuit. Surface dry suits are not inflated, and must be vented to remove most of the gas inside.

Because the air inside the suit is compressed as the diver descends, a modern diving drysuit also has a gas inflation valve, which lets the diver control the buoyancy of the suit by injecting gas from a diving cylinder to avoid the suit from being squeezed tightly and painfully onto the diver's body during descent. The sensation is similar to being pinched, but all over the body. Suit squeeze can also hinder the diver's movement and make swimming more difficult.

Some old-type frogman's drysuits had a small "jack cylinder" to be inflated from, or the frogman (who was using an oxygen rebreather and so limited to about 30 feet (9.144 m) depth) had to put up with the suit squeeze.

Normally, the gas used for dry suit inflation for diving is air from the primary breathing cylinder. When divers breathe helium-based gas mixes such as trimix, they often avoid inflating their suits with the helium-based gas due to its high thermal conductivity. They often carry a separate cylinder for this purpose; generally it contains air, although sometimes argon, which has lower thermal conductivity, is used. Pure argon cannot be used as a breathing gas. Alternatively, some trimix divers inflate their suits from a decompression cylinder containing a nitrox blend.

In surface dry suits, the wearer normally never dives deeply underwater, and is not concerned about neutral buoyancy, so there are no air valves on a surface drysuit.

The P-Valve

For commercial divers or technical divers who may spend many hours in a drysuit underwater, it is not practical to have to climb back onboard the ship in order to open a waterproof relief zipper and urinate. The P-valve is a urinal built into the suit, which lets a male diver relieve himself at any time without having to get out of the water, and keeping him dry and clean inside the suit.

Before putting on the drysuit, the diver puts on a condom catheter, which is similar to a condom except that it is made of thicker material with a cuff or adhesive ring to prevent it from slipping off, and its end connects to a built-on drain tube. After putting it on, he attaches the end of the tube to a drain hose in the crotch of the suit. This drain hose leads to a vent opening just above a knee, and may also have a one-way valve (P-valve)to prevent ocean water from flowing back in if the hose gets disconnected.

Divers intending to urinate in drysuits sometimes wear an adult diaper / nappy, which soaks up and retains the urine.

Uses of dry suits

Surface

Boating

Dry suits are often worn for boating, especially sailing, and on personal water craft in the winter months. The primary uses are for protection from spray, and in case of accidental short-term immersion in cold water if the user falls overboard. Dry suits only intended for temporary immersion protection are less rugged than diving dry suits. They are usually made of a breathable membrane material to let sweat permeate, keeping the wearer dry and comfortable all day. Membrane type surface dry suits only keep the user dry, and have little thermal insulating properties. Most users will wear a thin thermal undersuit, or street clothes, for warmth; but wearing ordinary fabrics can be dangerous if the suit leaks in cold water because they will lose all insulating properties.

Water sports

Dry suits are used for windsurfing, kitesurfing, kayaking, water skiing and other surface water sports where the user is frequently immersed in cold water. These suits are often made from very lightweight material for high flexibility. Membrane type suits are commonly used in the spring and fall with moderate water temperatures, but Neoprene and hybrid dry suits for surface sports are preferred in cold water. These provide greater thermal protection in the event of a leak. The ability to swim for self-rescue in these types of suits is important to water sports users that do not use a boat. A neoprene bottom also is less likely to allow trapped air to collect in the legs, causing the wearer to tend to float head down in the water.

Working

Crew members who must work on the decks of commercial ships wear a type of dry suit also known as an immersion survival work suit. Single engine aircraft ferry pilots flying between North America and Europe, and helicopter pilots that must fly over the open ocean, must wear a survival suit in the cockpit, so they can continue to fly the aircraft, then exit immediately if the aircraft is ditched in cold water after an engine failure. These suits are also used on shore when working on docks, bridges, or other areas where cold water immersion is a safety risk. They are usually a three-part system consisting of:

• A warm undersuit made of synthetic fabric designed to wick moisture from sweat generated by physical exertion away from the user’s skin.
• A dry suit made with a waterproof breathable membrane to let moisture permeate out of the suit.
• A durable outer shell, designed to protect the dry suit, and to carry tools and survival gear. The outer shell may also be equipped with an inflatable bladder to give the wearer additional flotation and freeboard when immersed.

Survival

Immersion survival suits are dry suits carried for use by ship and aircraft crew who will be immersed in cold water if the craft must be abandoned. Unlike immersion survival work suits, these are not intended to be worn all the time, and are only to be used in an emergency. Survival suits will typically be a one-piece design made of fire-retardant neoprene, and optimized with quick donning features.

Rescue

Dry suits are also worn by rescue personnel who must enter, or may accidentally enter, cold water. Features of dry suits designed for rescue may be a hybrid of the immersion survival and work suits, since the wearer is not expected to be working in the suit for an extended time. They may also be optimized for a specific task such as ice rescue, or helicopter rescue swimmer.

Underwater

Sport diving

Drysuits for sport diving are made in both membrane and neoprene, and primarily differ from surface drysuits in that they have inflation and deflation air valves to maintain neutral buoyancy, and are slightly more durable.

Commercial/military diving

Drysuits for commercial and military diving tend to be much heavier and even more durable than sport drysuits because they will endure a harsh and abrasive environment, especially if being used for heavy labor work such as underwater welding. Some commercial drysuits are rated for hazardous-environment diving, and when combined with a full-face helmet can completely isolate and protect the diver from hazardous environments such as sewage pits and chemical storage tanks.

Drysuit donning and diving hazards

Drysuit donning is usually more difficult than with a wetsuit and often requires the assistance of another diver or person. Drysuits pose their own unique problems compared to wetsuit diving, due to the complex construction and since a diver needs to constantly manage and adjust the air volume inside the suit. During descent, air must be added to maintain constant volume. This prevents suit squeeze, loss of neutral buoyancy, and potential uncontrolled descent. During ascent, air must be removed to prevent ballooning, loss of neutral buoyancy, and potential uncontrolled ascent. A drysuit can be equipped with an automatic spring-loaded exhaust valve, which can assist with this problem.

Seal damage

Latex seals are easily pierced by sharp objects. Gripping the seal with long fingernails to pull it on or off can cut through the material, while long toenails can damage thin rubber booties when the foot is pushed inside tight-fitting fins.

Some types of latex seals may be liable to rubber perishing.

Latex seals are somewhat elastic, but can be easily torn if overstretched. Powdered talc can help the seals slide on easier.

Neoprene seals are often used. They are less waterthight than latex, but can be repaired easily by the user.

Zipper damage

Waterproof zippers need the two rows of open teeth to be reasonably lined up in front of the pull, for the zipper to slide without excessive effort. (Because of their construction waterproof zippers require two or three times as much pull as regular zippers to close.) It is best to hold the opening together as the zipper is pulled shut to prevent misalignment that can permanently damage the sealing edge. For this reason zippers across the back of the shoulders or down the back of the suit are almost impossible for one person to close properly by themselves, and yanking harder to try and force the unreachable zipper closed often just results in misalignment and permanent zipper damage.

Suit damage

Damage to the lower part of the suit can cause a sudden inrush of very cold water for winter users, or an inrush of hazardous chemicals for commercial inspection divers.

Damage to the upper part of the suit can cause a sudden venting of the air, resulting in a total loss of thermal insulation in membrane suits and sudden uncontrolled descent, followed by water/chemicals seeping in.

Diving without a BCD

Since the drysuit can contain air, some divers control their buoyancy with the drysuit and dive without the usual BCD / buoyancy control vest that is commonly worn by wetsuit divers. Although it is possible to dive like this, the risks are higher than when using a buoyancy compensator, Drysuits generally are more easily damaged and prone to failure. Buoyancy compensators generally are more robust and reliable.

Inversion hazards

Underwater

If there is more air in the drysuit than is needed to counteract “squeeze” on the undersuit, that excess air creates a "bubble" which moves to the highest point of the suit, which in an upright wearer is the shoulders.

Drysuit wearers wearing loose baggy suits need to keep their legs at level or below their waist. When inverted, with the legs above the waist, the bubble quickly moves top the highest point, the legs.

If the suit is being used correctly, the bubble is small and its movement is not important. The bubble may be large if a diver has ascended without venting the suit or the diver is over-weighted and extra air has been put in the suit to make the diver neutrally buoyant. The movement of a large bubble can be a problem; it balloons the legs and it may inflate the thin rubber booties causing the fins to pop off, losing them in the water. Also, as the drysuit vents are most often situated at the top half of the diver, it is impossible to vent the suit while inverted. If the diver is positively buoyant, there is an increased risk of a fast ascent to the surface.

The size of the bubble can be minimised by being correctly weighted and venting the suit on ascent. Some divers ensure that the bubble remains at the top of their body by using the buoyancy compensator to counteract any excess weighting and keeping the minimum air, to avoid squeeze, in the suit.

For an inexperienced diver, ballooning of the legs can cause a loss of control that may to lead to panic and an inability to flip upright again. The recommended solution is for the wearer to bend at the knees, reach up and grab the legs, do a somersault to flip upright again and vent the suit if needed by opening the neck seal.

Surface

Surface drysuit users can face a similar inversion problem. The problem is more acute when not wearing a personal flotation device (life vest) over the drysuit. For surface drysuit users, the inversion situation can be much more critical if no one is nearby to assist, since the wearer may be held upside down and unable to breathe, and may also have water run down into their nose while inverted.

It is not a problem for close-fitting neoprene suits, or hybrid suits with neoprene bottoms, which prevent air from easily moving into the legs of the suit. Wearers of baggy surface drysuits can mitigate the problem by venting out as much excess air as possible before entering the water. This is typically done by crouching down and leaning forward, wrapping the arms around the knees, and then having an assistant zip the suit shut while it is stretched out tightly. Excess air can also be "burped" out of the neck seal. Some baggy suits have elastic "gaiters" that can be pulled snug around the legs to help prevent this inversion event from happening.

Early examples of drysuits

These suits are all the membrane type.

Maker	Make	1/2 piece?	When available	Notes	Info link
Pirelli	Pirelli Diving Suit	2	from 1930's	designed for Italian frogmen
Siebe Gorman	"Frogman" suits	1 or 2	World War II & after	designed for British frogmen rubberized stockinette
Spearfisherman	Spearfisherman Frogman Suits	2	1945 & after	designed for USA frogmen
U.S. Divers	U.S. Divers Seal Suit	1 or 2	from 1953 or before	varIous
Heinke	Heinke Delta Suit	2	from mid-1950s	rubberized stockinette
Healthways	Healthways Carib Suits	2	from 1955 or before	pure natural rubber
Bel-Aqua	Bel-Aqua Dry Suits	1 2	from 1955 or before	a 3-ply material, front tube entry a 3-ply material
unidentified	Seamless Suits	2	from 1953?	dipped pure latex
made by or for Lillywhites	Lillywhites Mid-1950s Suits	2	from 1955 or earlier	rubberized stockinette
So-Lo Marx Rubber Company	Skooba-"totes" Suits	2	from late 1950s	all-rubber
Siebe Gorman	Siebe-Heinke Dip Suit	2	1964 & after	dipped latex

References

See also

• Diving suit
• Wetsuit
• Sailing
• Watersports
• "Dry suit" as two words may occasionally mean a "suit which is dry" with the normal meanings of both words.