Table of Contents


Butch Hendrick and Andrea Zaferes

Drysuits, which can be made of several types of materials, encapsulate all parts of a diver's body, except for the diver's face. Surrounded by a layer of air in the suit, the diver stays totally dry, and is able to wear warm, insulating undergarment beneath the suit with a layer of insulating air. To compensate for the compression of undergarments and the air in the suit as the diver descends, drysuits have a power inflator much like that of a BCD. Because of the air within the suit and the additional power inflator, drysuits are a unique piece of equipment that, unlike wetsuits, require special training and certification. Besides the additional cost of training, a good drysuit will cost more than a good wetsuit. Still, drysuits offer many advantages to recreational, research, and public safety divers, including greater thermal protection, rapid dressing, ease of storage, and protection from hazardous materials. A good quality drysuit should last longer than a wetsuit.

Heat loss in water is largely due to conduction. So, a layer of heat-trapping, dry insulation in the form of drysuit undergarment greatly reduces that loss. Because the amount of thermal protection required can be changed by what divers wear under them, drysuits can be used for diving in any range of temperatures, from icy water to sun-heated ponds in August. Hence, the same piece of gear has applications for all diving seasons. If divers have drysuits, they should dive with them all year round so they can stay comfortable with them. Do not just wait until the more extreme types of diving in the winter.

Drysuits, with appropriate undergarment, will allow a diver to stay warmer for longer periods of time, both in and out of the water, than will wetsuits. Bear in mind though, that a vulcanized rubber or trilaminate drysuit alone has no thermal protection, so some type of undergarment is always necessary. Crushed neoprene also has little inherent insulation.

Drysuits will keep the diver warmer, especially at depth, because of Boyles' Law. The volume of a gas decreases as pressure increases. Wetsuits, which are filled with insulating gas bubbles, become crushed flat and lose thermal protection with depth. At approximately 4 ATA (4 BAR) a wetsuit will be half it's 1 ATA (1 BAR) thickness. A drysuit diver, however, can simply add air to the suit to maintain full thermal protection. Another advantage of drysuits over wetsuits is rapid dressing capability. Wetsuits must fit snugly in order to function, and therefore take a little longer to put on. Drysuits, however, have a looser fit. Well-trained public safety divers with good tenders can have their drysuits on before wetsuit divers even begin putting on the tops of their suits.

Protection from hazardous materials is another advantage of drysuits. Members of the public will forever find the concept of walking on water irresistible, and the cleanliness of that frozen water does not seem to be a concern. Public safety ice divers therefore are asked to dive in water filled with petrochemicals, pesticides, sewage, heavy metals, or other hazards. For those situations, drysuits offer a tremendous safety advantage over wetsuits, because they can keep these water-borne contaminants away from a diver's skin. For greater protection against hazardous material, the suits should be used with dry gloves, a built-in dry hood, and a full-face mask or diving helmet properly mated to the suit.

Drysuits can be easier to store than wetsuits. Wetsuits and neoprene or bi or trilaminate drysuits must be hung to dry after being used. Also, because the neoprene will crease, wetsuits must be stored on large hangers, which means they occupy a lot of space. A vulcanized rubber drysuit, on the other hand, never needs to be hung. Simply towel dry a vulcanized rubber suit, powder its seals, paraffin wax the zipper, and the suit can immediately be stored. A drysuit can roll fairly snugly into a small duffel bag that takes very little room - an important consideration when gear must be packed neatly, quickly, and efficiently into an apparatus truck. As with all exposure suits, do not lay heavy items on top of them during storage.

The myths of drysuit diving.

Many divers and dive teams have at least a few false beliefs about drysuits that prevent them from taking advantage of using drysuits and that may increase safety risks. Below are the most common myths, followed by the reasons they are untrue.

Myth #1: Drysuits require more weight than five or seven millimeter wetsuits.

In reality, a properly-weighted drysuit with warm undergarments may require the same or even less weight than a thick wetsuit. The key to weighting a drysuit is to vent excess air from the suit after it is donned. That way, the suit will have very little air in it when a diver enters the water, so the diver can descend with less weight.

Myth #2: Drysuits are more restrictive to movement than wetsuits.

A properly-fitting drysuit should allow full range of motion. Additionally, because they do not need to fit as tightly as wetsuits, drysuits are often more comfortable and less restricting. A key to having freedom of movement is to stretch arms fully up, forward, and then in a large circle to put the suit in the right place on the body before entering the water and once again when in the water.

Myth #3: To vent a drysuit that is malfunctioning and self-inflating, pull the neck or wrist seals out to allow air to escape.

While this procedure certainly sounds good, reaching through a hood or wrist seals while wearing gloves is extremely difficult at best, and to do it before hitting the surface may be impossible. Instead, if your inflator is stuck, first disconnect the hose, then purge air through the arm-mounted exhaust valve as you flare out to slow your ascent and do not forget to continue breathing normally.

Myth #4: Drysuit divers do not need to wear buoyancy compensators (BCD ).

While this procedure was commonplace years ago, it has been discarded. To be as safe as possible, drysuit divers should wear BCDs to allow them good flotation on the surface and to supplement the buoyancy of the suit underwater, if necessary. Drysuits were not designed to take the place of BCDs.

Myth #5: Add air to the drysuit and not the BCD for buoyancy control.

The philosophy behind this dangerous practice is that divers cannot properly vent or control both a BCD and drysuit during ascents, particularly uncontrolled ascents. One of the several hazards of only adding air to the drysuit is that this could cause an uncontrolled ascent if the diver is over-weighted, as the majority of divers are. Too much air added to a BCD can rapidly, easily and reflexively be purged. The same is not true for too much air added to a drysuit. A drysuit can hold far greater volumes of air than a BCD, so the mistake can be much greater. Air in a drysuit can become trapped in lower extremities, which could invert a diver and cause the loss of fins. This cannot happen with a BCD.

Pressure on a diver's neck caused by too much air in a drysuit can cause a carotid sinus reflex and possible unconsciousness. An over inflated BCD cannot do this, and a BCD has its own over-inflation self-purge valve. During ice diving, the more a valve is used, the greater the chance for free-flow. A free-flowing drysuit inflator poses greater risks than does a free-flowing BCD inflator. The safest procedure is to add just enough air to the drysuit for warmth and freedom of movement, and use the BCD to adjust for buoyancy.

Myth #6: A flooded drysuit will cause a diver to sink.

Water weighs the same inside and outside a suit, so the only way water can cause negative buoyancy is if the diver is very over-weighted and is using the drysuit (instead of the BCD) to compensate, and that so much water entered the suit that it replaced the air. Author Hendrick overweighed himself by 4-5 lbs (2kg). and then removed the inflator valve of a trilaminate suit he was wearing at 100 feet (30m) of depth. He discovered that the undergarments became stuck in the hole and kept water out. He then fully unzipped the suit and waved the opening in and outwards in an attempt to fill the suit. After filling the suit he made a slow, controlled ascent to the surface.1 In reality, the dangers of a flooded drysuit are contamination and hypothermia. Getting out of the water onto the ice roof may be a bit more difficult though if your legs are full of water. Use a sled or tender assistance should that occur.

Myth #7: Divers do not need a drysuit course and drysuit certification to dive in a drysuit.

Drysuits are a unique piece of equipment that require training and practice to use safely. Otherwise, divers risk drowning, carotid sinus reflex, decompression sickness, or lung overexpansion injury from improper drysuit procedures.

It is absolutely imperative that divers reflexively learn reality-based, effective self-rescue procedures for self-inflating/free-flowing drysuit inflator valves, and for inversion events. Students should experience swimming without fins on the surface with a fully inflated suit. They need to learn how to properly weight themselves for different thickness undergarments and varying amounts of air they will wear in the suit. A good course will teach them how to set the dump valve for different types of dives, and how and why to adjust it during a dive. Without good training, divers are likely to use poor drysuit dressing procedures which not uncommonly result in suit flooding, damaged zippers, torn seals, restricted wrist movement and circulation, and too lengthy dress times. Divers need to learn how to properly burp the suit prior to gearing up, how to dump air when at the surface, and how to stretch to make sure the suit sits on the body properly. Divers need to learn how to add enough air into the suit for warmth and comfort and then to make necessary buoyancy adjustments with the BCD, and how to adjust air in each with depth changes. A knowledgeable instructor will teach students drysuit maintenance and repair procedures to increase suit longevity, and will team them what kind of suit and features will best meet the needs of each student.

A good course will teach students how to properly cut neck, wrist, and face seals for increased seal longevity, increased diver comfort, and increased safety. Drysuit divers need to be capable of immediately recognizing signs of carotid sinus reflex in other divers and symptoms experienced by themselves. Sadly though, many of today's drysuit certification courses are somewhat lacking, which is why too many divers think that they do not need to become drysuit certified before diving dry. A good program is imperative. It is irresponsible for a diver to dive dry without good training, not only for the diver's safety but for the safety of anyone diving with the diver. Take the time to find good training, do not just take the first course that comes along.

A department or instructor that allows divers to dive in drysuits without drysuit certification is taking on a significant liability should a diver become injured or killed with the drysuit as part of the cause of the accident. Allowing uncertified drysuit divers to dive under the ice will be looked on as even greater negligence than if the divers were in open-water.

What to look for in a drysuit.

Fit: There are a variety of drysuits on the market, but one key factor to all of them is fit. Drysuits that are too big require more air internally to fill the excess space. This increases the amount of weight needed to dive and decreases overall mobility and diver safety. Mobility is based on the suit fitting properly and not compressing in areas such as elbows, knees, shoulders, and spine to the point of severe restriction. If the suit legs are too long, then the diver could lose one or both fins in the case of accidental suit inflation with body inversion.

Fit the suit with the thickest undergarments that may ever be worn, then bend down with hands reaching for the floor to make sure the torso is long enough. Stand straight with arms raised to the sky and make sure the crotch is not too low, which would mean that the torso is too long and possibly the legs are too short. With arms raised forward, make sure that the end of the suit material at the wrist does not extend beyond the wrist bone. Squat down to make sure the legs are long enough. Lay supine on the floor and have someone pull on the boots. If the boots come right off your feet then the legs are too long. With the warmest undergarments on, the suit should fit well to every part of your body. If it is necessary, suit customization is worth the extra cost.

Material: Full thickness neoprene offers the most intrinsic insulation but it has drawbacks. It requires a significantly greater amount of weight, significantly more time to dry, is difficult to repair on the scene, is more bulky to store, is not acceptable for contaminated water, and is more difficult to clean. Crushed neoprene suits have much less intrinsic insulation than full thickness neoprene suits but they are often more comfortable, easier to store, require less weight, and take a little less time to dry. They can be costly though, and have the same vulnerability to contamination, cause evaporative heat loss in air after immersion, and are difficult to repair in the field.

Bi or trilaminate suits require less weight, take less time to dry, are relatively easy to repair on scene before immersion, and take little room to store, but they offer no intrinsic insulation. The durability of trilaminate suits and their ability to protect a diver from contamination varies widely depending on the manufacturer and type of suit. Be wary about low priced suits because you will often get just what you pay for.

Vulcanized ethylene propylene diene methylene terpolymer (EPDM) rubber suits require the least amount of weight because they are intrinsically negatively buoyant. Less weight means less compensation for depth with the BCD , better buoyancy control, less risk of uncontrolled ascents, and safer diving. Rubber suits can be immediately repaired on scene even after immersion. Simply dry the area with a towel, sand a little, apply glue, wait a little bit, apply a little more glue, apply patch, roll with a soda can, wait a few minutes, and the suit is ready to dive.

Vulcanized rubber suits can be simply toweled off and then rolled for storage. These suits do not require any time to be hung to dry, which is a real plus for public safety divers who can simply replace the suits in their proper place after a dive to be ready for the next call. This ability to towel the suits dry is a great advantage for ice divers because the suits won't freeze between dives if there is no shelter, and divers can keep the suits on after a dive in wet weather since there will be no evaporative heat loss. If suits are shared between divers, the next diver can don a dry drysuit. These abilities are particularly important for dive teams who do not have the time or ability to set up a heated shelter on the site.

Viking Trelleborg TM manufactures vulcanized EPDM rubber suits that were the first to be approved by a rigorous series of testing with a multitude of contaminates. They used the National Fire Protection Association (NFPA) 1991/1994 edition of the standard for vapor protective suits for hazardous chemical emergencies and the American Society for Testing and Materials (ASTM) F1001 standard guide for chemicals to evaluate protective clothing materials, 1989. "It also should be mentioned that the only approval mechanism in place in the world today which does deal with standards of a diving suit, is CE95 0403. These are standards to which Viking is certified after passing through examination procedure in accordance with the Personal Protective Equipment Directive 89/686/EEC (PPE), class 3, which is the highest class with the toughest demands of the European Union."2 If contaminated water is a potential or realized concern then we recommend reading, Diving in Contaminated Water3, which includes the most comprehensive test data available on any drysuit for diving in contaminated water. Before purchasing a drysuit, ask to see data on testing for contaminated water.

Because of their impermeability to contaminates, vulcanized EPDM rubber suits are the easiest suits to clean thoroughly. With regard to durability, some high quality trilaminate suits may be more resistant to punctures and abrasion than vulcanized rubber, and especially neoprene or crushed neoprene suits. Make sure the suit comes with a good repair kit.

Zippers: Not all zippers are of the same quality. Again, you often get what you pay for. Ask what grade of zipper is installed in the suit. Use a heavier weight zipper (often referred to as heavy duty). Heavy duty zippers seal better and last longer than lesser quality zippers. They have larger teeth to the point of being almost twice the size of some medium quality zippers. Heavy duty zipper teeth are crimped and riveted into their rubber coated canvas base, while medium quality zipper teeth are only crimped. The downsides of heavy duty zippers include less flexibility and higher cost. The zipper will last longer if it is mounted on a rubber cloth material rather than a vinyl composite4.

A never-ending controversy is which is better, a front or back-entry zipper? Back-entry suits are usually more comfortable and easier to don. Since tenders should close all zippers, whether back or front, the advantage of a self-donning suit to public safety or ice divers is irrelevant. Front entry suits often require a flap of material that is buckled down over the abdomen. This is one more step for donning and more suit material to fill with air. Front entry zippers require a protective flap over them since they are more exposed to bottom and water debris than are back zippers.

Inflator and exhaust valves: Exhaust valves with a domed top are preferable to flat-topped valves, because the former can be purged by raising the left arm up, if the exhaust valves are on the left arm, and pressing the dome against the left side of the diver's head. This allows divers to disconnect a self-inflating drysuit hose with the right hand while simultaneously flaring and purging the suit. Again, check for valve quality because not all valves are created equal. A swivel feature in an inflator valve is good because it allows divers to position the inflator hose for the most effective and rapid disconnect move possible. The inflator valve should be pointed downward at a 45 degree angle for a center chest mounted valve, which is the most natural position to reach up and disconnect the hose in case the valve starts to self-inflate.

Suspenders and pee zippers: These are nice features to have, particularly for ice dive instructors and divemasters who may be in their suits for extended periods of time. Suspenders help hold the crotch of the suit in the proper position to allow full leg movement.

Cuffs and seals: Ice divers may want to have heavy duty latex cuffs and seals installed on their suits since cold increases the chance of latex tearing. Latex will tear more easily than neoprene, but it can be toweled dry and is better for contaminated water diving. Cuff ring systems are recommended because a torn wrist seal can be replaced in the field in less than a minute. If drysuits are shared by more than one diver, there are two options for individualizing neck seals. The least expensive option is to cut the neck seal for the diver with the largest neck and then have the other dives wear neoprene neck collars under the seal. Each collar would be of the appropriate thickness to make the suit neck seal properly fit the wearer. A second option is to purchase neck ring systems. Each diver has an individual sized neck seal that secures into the suit's neck ring. Cuff ring systems work well also for multiple-diver suit use. Each diver has appropriate sized gloves that are secured onto the cuff ring. The wrist seals are cut to fit the largest diver.

Drysuit undergarments: Always be prepared to be comfortable for longer than the planned dive time. Especially for public safety diving operations, divers may need to remain as back-up or 90%-ready divers for times longer than expected. Make sure the undergarment fits. If it is too tight it can restrict movement and blood flow. Even an undergarment that is too big can cause movement restrictions and decreased circulation. For example, if the torso is too long, the crotch area may end up too low, making it difficult to kick well, or if the legs are too long, they can bunch up at the ankles causing decreased circulation to the feet.

Avoid undergarments with a great deal of compressibility, which will result in unnecessary and possibly hazardous buoyancy changes if your diving will occur deeper than 33 feet (10m). Pile-type undergarment, for example, will greatly compress with depth, making the diver heavier. The diver responds by adding air to the BCD, which makes buoyancy control more difficult and the chances of rapid ascents more likely. And remember: rapid or uncontrolled ascents under ice are far more hazardous due to the overhead environment.

Choose undergarment material that will work when wet, so divers will not become chilled in case they exert themselves and sweat before they dive, and in case the suit leaks for whatever reason. Polar fleece and wool works very well. An Acrilian pile undergarment was tested under an immersion coverall during immersion for one hour in 2.5C (36F) water. Subjects without the undergarments lost 13.1oC (55.6F) of mean skin temperature while the protected subjects only had a loss of 9.9oC (49.8F) 5. Avoid anything cotton because once wet or damp, divers will quickly chill. One study tested three types of undergarments: cotton, polyester, and teviron, worn under a drysuit in 10oC (50F), 7oC (44.6F), and 5oC (41F). Today's more popular undergarment materials include Thinsulate TM for wicking away moisture and Moleskin TM. A wetsuit was also tested. Rectal temperature, skin temperature, exhalation volume, and decrease in body weight were the variables investigated. "Teviron undergarments provided the best heat insulation and the wetsuit was the worst." 6

Drysuit Maintenance

If the water has any level of salt or contamination, the suit should be washed down with freshwater, or with water and Joy TM liquid soap and then rinsed. Ask the suit manufacturer if there are any cleaning fluid recommendations specific to the suit you have. If dirt has settled in the zipper, brush it out gently with a soft toothbrush.

If a suit becomes wet on the inside, either due to diver perspiration or suit leakage, the inside must be dried before the suit can be stored. If the suit has been stored without drying the inside and mold has begun growing on the inside, sponge it down with a 5 percent bleach solution, and then rinse with freshwater before drying. Suits that are naturally heavy, or that become heavy when wet, such as inch (6 mm) neoprene drysuits, may develop stressed horizontal seams if hung to dry. Such suits may last longer if they are laid to dry across a fire department hose rack or even a few chairs. A fan may be used to decrease the drying time.

Once the suit is dry, generously powder the inside and outside of all the seals with pure talcum powder. The best source for talc is a store that specializes in large farm machinery. They sell large containers of talc at a fraction of the cost paid elsewhere. The talc can be placed in cloth sacs for ease of use. Avoid inhaling the talc when applying it. Talcum powder will make the seals slip on the diver much easier with less strain on both the seals and the diver, and will help prevent dry rot during storage. Avoid powder with scents or oils7.

Next, lay the suit zipper-side up on a flat surface with the zipper closed. Rub paraffin wax into the sides of the teeth and then open and close the zipper several times. Repeat this process until the zipper closes smoothly and effortlessly. Do not wax the inside of an open zipper because that wax will not wash away during a dive, and will therefore accumulate. If the zipper has been poorly maintained, do not force it closed. Carefully wax the sides of the teeth with it open and gently close it. The zipper is the most expensive part of the suit, and replacement costs can cost as much as one third of the suit's value, so proper maintenance is important.

Never use beeswax on the zipper because it will allow dirt to stick to it that can cause the teeth to bend when the zipper is opened. If beeswax has been used on the suit clean it out with a toothbrush and perhaps a solution with Joy TM liquid dish soap. Some manufacturers recommend commercially available zipper lubricants other than beeswax. Our experience of thousands of ice and warmer water dives with zippers solely lubed with paraffin has shown us that paraffin wax works well. We have had vulcanized rubber suits dry rot after twenty years of use, without ever needing to replace a zipper. Purchase a block of paraffin wax at a hardware store, cut it into slices, place each slice in a Ziploc TM bag and then store one with each drysuit.

An effective procedure to ensure that all divers have properly waxed suits is to wax the zippers after a dive before the diver removes the suit. Keep the zipper closed, wax it, then remove the suit.

If the zipper develops loose threads sticking out from the stitching, carefully cut the threads without pulling on them. If there are many loose threads, send the suit in for repair.

After the suit is dried, powdered and paraffined it is ready to be rolled and stored. Store it with the zipper open to prevent unnecessary zipper strain that will decrease the life of the zipper.

1 Walt Hendrick, Drysuit Flooding Video ( Delphin Productions 1983)

2 V DiGiglio Diving in Contaminated Water, just how safe are you? (SORTIE vol 1, issue 3, 1999)

3 available at no charge from Trelleborg VikingTM.

4 Trelleborg Viking

5 Marcus, S Richards, Effect of clothing insulation beneath immersion coverall on the rate of body cooling in cold water ( Aviat Space Environ Med 1978) 49, p. 480-483

6 K Tomiyasu, M Nakamura, M Yamada , T Murai, Study of body heat loss and heat insulation or heating on a diver: effects on heat insulation of undergarment for dry diving suit ( JAMSTEC 1980), 5: p. 187-199.

7 As per manufacturer such as Trelleborg Viking TM.

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