Why Dry?

Why do I need a Drysuit?

drysuit.jpg (8938 bytes)Why do I need a drysuit? If I had a dollar for every time I have been asked this question since I started diving in 1981, I could buy that house in north Florida that I have had my eye on, right now.  To understand why a drysuit does such a better job of keeping you warm, it is important that you (the diver) understand a little history of thermal protection for diving.


Ever since the first person donned a face mask, divers have been trying to insulate themselves from and yet enjoy the underwater world. The first suits used by by divers were crude "drysuits" that were, in actuality, just large bags made of rubber, treated canvas or animal skins.

As diving progressed, the closed cell neoprene wetsuit became the suit of choice for the recreational diver. while the commercial and military divers never discarded the drysuit, for reasons that will become clear as we go along.

Todayís recreational divers are now starting to ask why the commercial and military divers are using suits that are so much different from their good old wetsuits. Especially since ... they cost more .... arenít that much warmer ... have delicate seals and zippers ... require specialized training ... and I donít get cold in my wetsuit anyway.

Neoprene Wetsuits

Closed cell neoprene has its origins in the air conditioning industry. The material was widely used in Naval combat ships to insulate their sensitive electronic equipment from extreme temperatures during World War II. After the war, enterprising amateur divers tried some of the material to form an artificial insulated "skin" that would make scuba diving more tolerable.

Closed cell neoprene is just as the name implies ... closed cell. It consists of thousands of tiny bubbles of gas that act as individual insulators. The neoprene "rubber" itself acts as a water barrier.

The most widely accepted theory as how a wetsuit works is that the thousands of tiny bubbles act as insulators to minimize the heat transfer from inside to the the outside of the suit surface. Additionally, the thin layer of water that is trapped between the body and suit is warmed by the body and acts to slow subsequent heat loss.

Closed cell neoprene does a good job of minimizing the heat transfer across the material. However, the effectiveness of a wetsuitís insulating qualities diminish under the following circumstances:

  1. Age:

As rubber ages, it becomes hard and brittle. The cell walls are subject to cracking and will eventually pass water through it much like a sponge. If you were to ask the average diver " How long to you think that new wetsuit you just purchased is good for, what is the life span?", you would most likely get answers of anywhere between one and twenty years.

The reality of the situation is neoprene shrinks from the day that it is made. If a person purchased a new wetsuit right now, assuming that that wetsuit fits properly at the time of purchase and assuming that the person does not gain or loose a single pound of body weight, and that the wetsuit is cared for, in a best case scenario it will last a maximum of three years. If you find that hard to believe, then go to your local dive site and watch divers getting dressed. Most divers that have a wetsuit that is more than a year old will struggle to get dressed into it. I have treated a number of "HEART ATTACKS" by having the diver unzip their wetsuit that is two sizes to small. Please keep in mind that a tight or baggy wetsuit does a very poor job of keeping you warm.

  1. Decomposition

Chemicals and gases, primarily chlorine and ozone, attack the rubber, causing embrittlement or sometimes making the rubber turn to a liquid goo. The sun also enbrittles the rubber. Even the gas that is used in the manufacturing process to make the bubbles can sometimes cause the rubber to deteriorate. ( Note: this does not happen with nitrogen blown neoprene) As the material gets harder, the bubbles crack ... as it gets gooey, the bubbles collapse.

  1. Compression

By taking the neoprene underwater, we are subjecting the gas bubbles to increased pressure. As we learned from beginning SCUBA class, when the pressure increases, the volume of the gas bubble decrease. This translates to reducing the thermal insulating capabilities as we go deeper. Additionally, of the thousands of tiny gas bubbles that are compressed from the increased water pressure, some will burst and others will stay collapsed afterwards. Wetsuits are also subject to linear compression ( folding or creasing ) which collapses the gas bubbles at the fold when they are in storage.

NOTE: This will also happen to foam neoprene drysuits I in the above section "age" I stated that under a best case scenario, your wetsuit would last three years. You may not get three years out of your wetsuit if you dive often and the neoprene becomes compressed. This would be like removing one half on the insulation in the walls of your house on a cold winter night.

Neoprene is made in sheet form and has itís greatest insulation qualities when it is laid flat against the surface it is to insulate. When the wetsuit is on the body this is no problem, but after a dive the suit needs to be properly stored to prevent creasing. Hanging, even on the widest hanger, causes the shoulder area to stretch out under the weight of the suit and lose some of itís insulating abilities in that area.

Rolling or folding causes creases which may stay compressed and cause insulation loss along the fold. Wetsuits are best stored in a cool dark place with a form inside to keep the material from folding up on itself.

Water layer- Water has an excellent heat transfer coefficient which means it transfers heat fast! That thin layer of water that is trapped between the body and the suit robs the body of heat and reaches a point where the water is approximately the same temperature as the skin itís stealing heat from. At that point, we are relying on the insulating capabilities of the neoprene to keep water layer from cooling down. This works fine until we make the mistake of moving! Movement pumps the "preheated water" around inside the suit where it is free to escape at the zippers, wrist and leg openings, neck and waist. The warm water is replaced with cold water and heat robbing process starts all over again.

Wetsuits work fine to maintain the bodyís core temperature as long as we follow these simple guidelines:

  1. Donít wear your wetsuit any deeper than you would be willing to swim with just a lycra skin on.
  1. Donít subject your suit to salt, pool chemicals, sun light, heat or air. When storing the suit, seal it up in a air free, nitrogen filled bag and keep it in a cool dark spot.
  1. Donít expect to get more that three years out of your wetsuit.
    Note: A new wetsuit will cost your between $200.00 and $500.00 depending on if you are a custom suit or you fit into a stock suit, off the rack suit.

Please remember that one way you can tell if your wetsuit fits you is to put it on. If the zipper teeth do not lay next to each other with some "HELP" then the wetsuit is too small.

  1. When wearing your wetsuit ... DONíT MOVE!


The human body is a very special machine. It senses when we have too much heat and sends blood to the surface of the skin to be cooled by perspiration. When this happens, the skin becomes very soft and supple; most noticeable in the neck area. If the body is losing too much heat, it begins restricting blood flow so as not to cool down the vital organs ( core temperature ) . In order to maintain core temperature, the body first restricts blood flow to the extremities, which manifests itself as cold hands and feet. Should the temperature continue to drop, the body starts generating heat by causing the muscles to move very quickly and erratically ( you are now shivering )

The process of maintaining core temperature consumes enormous amounts of energy which in turns makes the body tired and less able to combat the heat loss.

NOTE: When a diver gets cold as described in the above paragraph, he or she will start to produce a very high amount of urine. This sets-up the dehydration journey that greatly increases a divers chances of getting D.C.S. (decompression sickness).

Unearned Fatigue

In a wetsuit, as much as 40% of the energy consumed during the dive is the body just maintaining the core temperature, as compared to only 10% for a diver in a drysuit.

Example #1:
Joe and Jim dive for one hour in 45F water and swims for 50 yards. Both divers are in identical shape and use the identical equipment with the only exception of the exposure suits. Joe is in a wetsuit and Jim is in a drysuit. At the end of the dive Joe has burned 1,000 calories while Jim has burned only 667 calories.

In the example, the swimming and underwater activity of both divers burn 600 calories in each one. In Joeís case, he has burned an additional 400 calories (40%) just maintaining his core temperature. Should these divers make two dives, Joe will have burned 2,000 calories while Jim will have only burned 1,334 calories. For three dives, Joe burns 3,000 and Jim burns 2,000, and so on. If we do the math, we can see that Joe will be as tired after his second dive as Jim will be after his third.

Example #2:
Joe normally makes two dives a day in 45F water and is completely spent by the end of these dives. On a trip to Cozumel, he drift dives in 86F water. He makes a number of dives per day. And at the end of the day he still has energy left over. The obvious question is why. Joe is not burning calories to stay warm in Cozumel, the way he is back home. If you were to take a boat load of divers out in the Northeast and give one half wetsuits and the other half drysuits, all things being equal, the wetsuit divers most likely would be sleeping on the ride home and the drysuit diver would be playing cards or watching a good video.

In Conclusion:

Diving warm and dry is a comfort issue, I believe that the #2 reason why people drop out of diving, (#1 is poor or inadequate training), is because they are cold and uncomfortable. How many times would you go skiing if you were cold and wet? Diving warm and dry is also a safety issue. If you take a diver and get he or she cold and tired, how do you think they are going to do when it comes to making decisions or, God forbid, an emergency arises and they are forced to deal with it?

Special acknowledgement to Ray Contreras, Sr. sales representative for O.S. Systems inc.
Any comments about this article should be directed to Frank Copren. (631) 277-8636