How do wetsuits work? Wetsuits provide warmth using a layer of waterproof insulation between your body and the external cold water.
Determining the thermal protection offered by a wetsuit is complex:
- How much of the body is covered,
- Temperature gradient between the body and the surrounding water,
- Duration of partial immersion (in the water on the surface) and total immersion (dive duration),
- Level of physical activity,
- Internal and external water exchange,
- Volume of water pooling within the wetsuit,
- Insulator material,
- Insulator thickness,
- Liner material, and
- Seam seal effectiveness.
Whether a given level of thermal protection is comfortable or not is entirely subjective, depending on the sensitivity of the individual.
What follows is an indicative guide to how different facets of wetsuit design effect thermal protection and comfort.
Neoprene (polychloroprene) is available is a wide range of grades which rate the size and density of individual cells, and the proportion of neoprene to butyl rubber.
Neoprene is a rubber sponge. The rubber is a matrix of closed cells which are like individual gas filled bubbles. To create the cells, rubber is mixed with a chemical blowing agent which reacts with the rubber under heat and pressure to generate nitrogen or carbon dioxide.
The size and density of individual cells will affect the weight of the suit and the compression under pressure. For a given material such as neoprene, thermal insulation will depend upon the thickness of the insulator. As the neoprene becomes compressed with increased pressure at depth, it offers less and less protection as you get deeper.
Neoprene may also be blended with butyl rubber for elasticity.
Inner and outer linings
Wetsuits are made from double lined neoprene, which has a layer of material on each side for comfort and durability.
The outside layer will be durable, water repellent, and flexible; usually stretch nylon or Kevlar as armour against damage and protection from sunlight (UV radiation degrades neoprene). High wear areas such as elbows, knees, and buttocks can be further reinforced to help prolong the life of the suit.
The inside layer will be flexible and insulating; usually stretch nylon to reduce friction over body parts. Some manufacturers include a layer of titanium lining as an additional insulator said to reflect heat.
Some wetsuits are made with an inner plush lining or fleece layer, softer and more comfortable than stretch nylon, and slows water circulation within the wetsuit.
Body coverage and insulator thickness
|Bikini or boardshorts/budgee smugglers
||(1mm | 0.039in)
||>29C | >84F
|Shorty (torso, upper thighs, and upper arms)
||(3mm | 0.118in)
||26-28C | 78-83F
|Full Length Steamer
||(3mm | 0.118in)
||22-25C | 71-77F
||(5mm | 0.197in)
||13-21C | 55-70F
|Full Wetsuit (inflexible)
||(7mm | 0.276in)
||<12C | 54F
* indicative temperatures only based on a 1 hour dive.
Some wetsuit designs will use a mix of different thickness for different panels, so the torso will prioritise thermal protection with thick insulation, while the limbs prioritise range of movement with thinner insulation.
- Over lock – cheap and durable, water seepage through lots of holes, not comfortable. Common in hire equipment.
- Flat lock – more expensive, very strong, water seepage through lots of holes, stitches lie flat and so are comfortable against the skin.
- Blind – Stitched with a curved needle that does not penetrate all the way through to the other side. Creates a stitch with no holes for water seepage.
- Double blind – Blind stitched from both sides.
Other joinder and sealing techniques:
- Gluing – Gluing two panels of neoprene together along their edges.
- Taping – Applying an adhesive tape over stitches for a final watertight seal, to protect the thread from damage, and to avoid skin abrasion from contact with the bare stitching.
- Liquid seal – Applying a liquid rubber over the seals, which sets as a watertight but flexible coating.
- Fusion – Newer glues may be strong enough to hold a wetsuit together without stitching.
These techniques are used in different combinations for the following seam sealing methods:
Flatlock stitching – For shorties and tropical water the low cost flatlock stitching will be sufficient. It will let a little water seep into the suit but with negligible effect in the warm water. The stitch will lie flat against your body and not cause rubbing marks.
Sealed (glue and double blind stitch) – For full length steamers and 5mm | 0.197in full wetsuits. The seal will be durable and comfortable, letting in very little water.
Sealed and taped (glued, double blind stitch, taped) – For 5mm | 0.197in and 7mm | 0.276in full wetsuits. The seal will be watertight, very durable with 3 methods of reinforcement, and comfortable with the tape covering all stitching.
Front zipper vs back zipper
Wetsuits with back zippers are usually intended for or based on surfing wetsuits where the surfer’s weight will press down on the front of the wetsuit against the surfboard and a front zipper would cause great discomfort. For this reason surfers want a clear chest piece and locate the zipper on the back where it will not be pressed into the body.
The weight of back-mounted scuba equipment will press down on the back of the wetsuit against the diver’s back, causing discomfort. For this reason, scuba divers want a clear back piece and locate the zipper on the front where it will not be pressed into the body.
For scuba diving, a back zipper requires assistance for dressing and undressing, or a pull cord that may become entangled in the complex equipment around it. Front zippers can be easily operated by a diver without assistance and so are both safer and more convenient.
Plastic vs brass
Modern polyurethane zippers are not easily damaged and maintain a smooth action over time (without degradation and tearing of surrounding material which occurs with the old style brass zippers).
Properly fitted, firm, gently squeezing you all over but not uncomfortable. Too tight and you will be uncomfortable and movement restricted: too loose and water will pool in the loose spots, increasing the volume of water to be heated by your body and heat loss, plus constant circulation of external cold water.
Unless a dry-zipper is used, then the zipper will be a main point for water to enter the wetsuit.
These are wetsuits made with bare neoprene or other waterproof seals at the ankles, wrists and neck. Semi-dry wetsuits allow water to fill the spaces between the body and the suit so do not require equalisation like a drysuit, but do not allow the water to circulate with the outside water like a wetsuit. The inside water will warm to body temperature and since there is no circulation with the outside water that heat is not lost.
How to make sure a wetsuit fits properly
A wetsuit which is too small will be very uncomfortable, restrict breathing and blood flow, and restrict range of movement. A wetsuit which is too large will require extra weight to achieve neutral buoyancy, and will let in too much water and allow too much water circulation to provide adequate thermal protection.
To test whether a wetsuit fits properly:
- When zipped up there should be no excess room, including around the torso, crotch, shoulders, and knees. A properly fitting wetsuit will be firm, lightly squeezing the whole body, but not so tight as to be uncomfortable.
- Range of motion test (from a standing position):
- Raise your arms as high as you can above your head, one at a time then both together;
- Touch the back of your neck (as if grabbing the cylinder valve) with each hand, then with both hands at the same time;
- With feet flat on the floor and shoulder width apart squat down, bending hips and knees, until resting on your haunches;
- Touch your toes with both hands, bending at the waist;
- Kneel down with one leg raised as if in a lunge, try with each leg; and
- Stand with legs at twice shoulder width apart to make sure the crotch is the right height (if too low then the movement will be restricted).
ABOUT DIVING GLOVES
Our Advice: 1mm | 0.039in neoprene with rubber grip on finger pads and palm, no elastic and/or Velcro straps, and cut off the first joint of the thumb and index finger (sewing up the seams so they do not unravel).
Thin gloves made from neoprene (1mm | 0.039in) and other materials are resistant to the elements and will protect your hands from cuts and abrasion. Although you should not be touching the marine life anyway there are still sharp rocks and barnacled lines to deal with.
Cave divers and photographers cut off the first joint of the thumb and index finger of the neoprene gloves to make manipulation of lines and equipment easier (unless the water is too cold). Once you have cut off part of the finger you must also sew up the remaining seams so they do not unravel.
Thicker neoprene gloves or mittens (3-5mm | 0.118-0.197in) are available for cold water, but the diver will lose a lot of dexterity and all sense of touch.
Rubber or other high friction material patches on the finger pads and palms are necessary for grip and to manipulate equipment while wearing gloves.
ABOUT DIVING BOOTS
Our Advice: 3mm | 0.118in neoprene; reinforced heel, toe, and top of foot; zippered with Velcro retaining tab; and thin rubber soles.
Neoprene dive boots are available in 3-5mm | 0.118-0.197in thickness.
There should be rubber reinforcement on the:
- Heel to protect against wear from the fin strap,
- Toe to protect against wear from walking around and accidently kicking stuff, and from the front of the fin foot pocket, and
- Top of foot to protect against wear from the top edge of the fin foot pocket.
Zipper vs pull up
Pull up dive boots may also pull off while fining. Zippers are more secure, but it is preferable to have a Velcro tab at the top of the zipper to make sure the zipper does not work itself open while moving your feet about over the course of a dive.
Thick rigid sole vs thin flexible sole
Thick rigid soles are heavy, negatively buoyant, and do not fit many fin foot pockets. They are said to be good for rugged entries, but in reality few divers will encounter the kind of sharp rock barrier that would justify these soles.
Thin flexible soles provide more than adequate foot protection for rocky shore entries. They are also lighter for travel, slightly positively buoyant, and fit well with most fins.
Hoods are available in 3-5mm | 0.118-0.197in thicknesses and go a long way to preventing heat loss underwater.
When exhaling underwater bubbles will pass the hood edges around your face and some air will work its way inside to accumulate at the back of your head. This problem is solved by flattening the hood so that the sides touch, and make several cuts (not holes) along the fold which runs along the back of your head between your crown and the top of your neck. The cuts will lie flush and closed unless there is water behind them, in which case they will open enough to let the air escape.
STAYING WARM ON THE SURFACE
To stay warm after the dive or between dives, remove your wetsuit from at least your upper body. On the surface a wet wetsuit will rapidly transfer heat from your body as the moisture evaporates from the outside layers (evaporative cooling).