Drysuits are commonly divided into foam neoprene, vulcanized rubber and urethane coated fabric. Most drysuits normally require undergarments to enhance insulation and improve moisture control. Although diving undergarments can be costly, such materials are an absolute necessity in advanced diving activities.

The really good news of the ’10s about drysuits is that the price has come down, they are well built and rugged and there are lots of choices of styles, sizes and features. Last month’s column covered the history and theory of drysuits.

Drysuit Materials

The most common materials used for drysuits are vulcanized rubber, foam neoprene, crushed neoprene, urethane coated fabrics and tri-laminates. There is no single “best choice” – each has its own pluses and minuses, depending upon how and where you dive. We’re going to discuss the three basic types of suits, vulcanized rubber, foam neoprene and urethane coated fabric. The other suits on the market are variations of these three.

Vulcanized Rubber

Although rubber drysuits have been around quite a few years, there is a lot of technology in making seams that stay waterproof, rubber that lasts and a fit that is desirable. Vulcanized suits are made of a rubber compound that inhibits ozone deterioration and is not too elastic. The inside is covered with a soft fabric to make donning easier and to absorb body moisture. The neck and wrist seals are usually latex rubber, as this bonds to the suit easily.

It is manufacturing equipment intensive to produce a heat sealed seam suit. The seams in a better vulcanized suit are actually fused under heat and pressure. The suit is loosely stitched to hold the pieces together, then placed on an aluminum form for the heat treatment. Better suits are made by applying tape to the seams after the suit is on the form. It obviously takes a very large heat and pressure chamber to put several full sized suits on mannequins for processing. It is possible to merely glue together pieces of vulcanized material but this does not produce as high a quality suit as one with heat treated seams.

Because of the need for an aluminum form for each size of heat treated suit, the standard range is limited. These suits tend to fit loosely as everyone tries to make a limited size range work. Custom tailoring is possible. After a suit is manufactured, it can be altered to add or subtract fabric but the new seams will show. Vulcanized rubber drysuits vary in weight from very light to heavy duty commercial models.

Materials and undergarments

Foam Neoprene

Foam neoprene drysuits are typically the least expensive. They are manufactured by local and national companies that also make foam neoprene wetsuits. These types of drysuits are pattern cut from rolls of fabric, glued with wetsuit cement, then blind stitched to strengthen the seams. Blind stitching does not penetrate the material so watertight integrity is preserved. Some companies also coat or tape the seams to improve watertight integrity. The suit is made watertight with neck, wrist and leg seals of thin neoprene and a special zipper.

These suits may have a low pressure inflator hose attachment or a corrugated hose and oral inflation mouthpiece like a buoyancy compensator. The disadvantage of an oral inflator is that when you push the exhaust button, water will normally enter the mouthpiece and trickle into the suit. Many divers using these suits wear a T-shirt underneath to soak up this water.

Neoprene suits are close fitting and most divers do not use thermal undergarments with them. Thermal protection relies on the normal properties of neoprene. All the environmental conditions that “wear out” wetsuits affect neoprene drysuits. Over time the cells in neoprene break down and collapse from ozone, heat, age, repeated bending or abrasion. As the material breaks down, it begins to leak and loses insulating value. Punctures in a neoprene suit can be repaired with wetsuit cement but are sometimes hard to locate. The suit needs to be totally dry to do wetsuit cement repairs and it can take hours or days to get the suit truly dry. These suits typically have one water and pressure proof zipper across the back of the shoulders.

A neoprene suit typically lasts three to five years or 200 to 400 dives, depending upon how hard you are on a suit, air quality where you live and how well you take care of it.

Urethane Coated Fabric Drysuits

Urethane is a synthetic material that can be applied to nylon, creating a waterproof fabric. The quality of a urethane suit can vary tremendously with the weight of the nylon fabric used. The heavier the fabric the sturdier it is and the more resistant to abrasion. Nylon fabric is graded by denier, or weight of the fabric. For example, a 420 denier nylon is heavier than a 210 denier fabric. Denier is an old French term for a unit of weight of threads equal to .05 gram per 450 meters of the thread.

Urethane drysuits are flexible but have no stretch. This is one of the reasons they are baggy – otherwise you could not get in and out of the suit. Urethane suits are cut from a pattern and sewn together just like clothes. The easiest way to waterproof the seams is to seal them all with a machine that welds urethane tape over them. A more expensive construction technique folds the seams twice and then stitches them. This technique is labor intensive and requires more material but it produces a more reliable seam that is less likely to pull or leak.

Urethane coated fabric suits last five or seven years of normal sport diving with reasonable care. When the urethane starts to break down you’ll see spider web sized cracks appear and feel the trickle of water. Then it’s time to shop for a new suit.


It is tough to find one style and weight of drysuit underwear that is going to be perfect for every diving situation. Diving underwear can be expensive but it’s absolutely essential for most drysuits.

Plan your undergarments on the layering concept. A first layer might be a lightweight jumpsuit and the second layer could be a vest. It is essential to know your suit, the water temperature and your planned activity. Since you can’t take off or put on a layer underwater, you have to plan ahead.

Drysuits work on the principle of passive insulation. Drysuit underwear traps a layer of air warmed by your body heat. The miniature air pockets in the structure of the wool or synthetic material determine how good an insulator it will be. In general, the thicker the undergarment, the more air pockets it has and the warmer it is. However, some materials are not only very thin but great insulators – so the rule is not an absolute guide.

In addition to a material’s insulation capacity, it is important to understand how it responds to moisture. When you perspire underwater this warm moisture condenses on the colder inside of the drysuit. If your undergarments (like cotton long johns) soak up this moisture, you will feel cold and clammy. It has been described as “wearing a wet body diaper.”

Undergarments come in one piece jumpsuit styles and two piece tops and farmer john bottoms. It’s a matter of personal preference and knowing how sensitive you are to temperature. lt is easier to adjust via layering a two piece set than a jumpsuit. Whichever style you choose, fit is extremely important. You have got to be able to move freely – bend over, squat or climb a ladder. If your flexibility is reduced by the underwear, it will be even worse once the drysuit is donned.

Pockets are a nice feature as long as they are placed so their contents don’t jab you. Also, think before you put things in an underwear pocket that could leak, implode or punch a hole in your suit when under pressure. Car keys, lighters and pens have all produced interesting accidents.

Boots are a big consideration. They need to provide adequate insulation, survive rough use if you walk a distance after suiting up, need to resist compression and may need to be laundered more often than the rest of your underwear. The soles and the sides of the boots need to be water resistant so you can leave the boots on between dives without soaking up beach or boat deck water.

Washing Undergarments

Read the instructions on the garment and follow them exactly. They may ask you to do some things that seem silly but there are reasons related to how the garment will absorb water after the washing. Soap acts as a wetting agent, which allows oils and dirt to be washed out of a garment. That’s good. If you fail to completely rinse the residue out of a drysuit undergarment, the dried soap stays in the suit and continues to act as a wetting agent during your dive. That’s bad.

Use very little soap to start with and then re-run the rinse cycle several times. If your underwear starts developing a “rubber” smell, add a tablespoon of bleach in the wash cycle. Unless you want bleach spots on your suit, wait for the washer to fill with water before adding the bleach.

The best way to dry the undergarments is on a plastic hanger (no rust spots) in the air. This is slow. You can speed the drying by using the air fluff cycle of a clothes dryer. Your suit – like all clothes – loses some lifespan every time your machine dry it. Don’t use a heated dryer on certain synthetic materials as it can cause the fibers to melt and thus reduce its insulating effectiveness.

Wooly Bears

Named after the original wool long johns worn by commercial divers, wooly bears are now synthetic and nonitchy. Polyester wooly bears are a great choice today. They are comfortable, good insulators and do not pill. Dry, 16 ounce polyester wooly bears are fine for 60oF  water. The drawback is that wet polyester has almost no insulating ability. Wash polyester wooly bears in very little mild soap and air fluff (no heat) in the clothes dryer or hang out to air dry.

Manmade Fibers

Manmade fibers can surprise you. I always thought of polypropylene as yellow waterski rope – turns out it is used to make fabric for mountaineering clothes, too. A polypropylene liner adds insulation and helps wick moisture away from your body. This reduces that clammy sauna suit feeling. Some divers use a liner and sweats under their drysuits for warm-season diving, such as the 65 to 70oF water of a Southern California summer. If you wear sweats under a drysuit, be sure to select a synthetic fabric, not cotton. Synthetic sweats are tough to find but cotton soaks up sweat easily, then rapidly conducts heat away from your body.

Many outdoor sports have benefited from 3M Corporation’s development of lightweight Thinsulate. Undergarment makers sandwich Thinsulate between other fabrics, such as nylon and fleece. The nylon allows your drysuit to slide on easy and the fleece feels nice next to your skin.


If you can keep your torso warmer, it helps maintain your core body temperature. If undergarments were made of thicker material to provide this extra protection for your chest, you’d have a hard time bending your arms and legs. So, a vest is an ideal solution. Since the vest will be worn on top of another undergarment, remember you may need a bigger size. Try on all the pieces you plan to wear. You don’t want to feel stuffed or have your movement restricted. Also, insulating materials work by trapping tiny pockets of air, so don’t layer clothes so tightly you eliminate all the air spaces. Vests are made of pile material or are a nylon shell with fiber fill inside.


Many drysuits are the vapor barrier and require undergarments to enhance the insulation value. If you select something other than a foam neoprene drysuit, you’ll also need undergarments for added warmth. Throughout this article “how” the suits are made was stressed, because of the importance of the seam integrity. Short of a puncture or a ripped neck or arm seal, suits develop their first leaks at the seams. Seams take a lot of stress as you put the suit on and take it off. The torture test continues as you kick, crawl, climb out of the water, hang the drysuit from the shoulders to dry and then finally fold or roll it into a bag for travel. A leaking seam in a foam neoprene suit is an annoyance; a trickle of water that gets soaked up by undergarments is a heavy mess. Only an ultra-dedicated diver will crawl back into wet undergarments for another dive.

Be with us next month for the third and final installment in our series on drysuits.


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