Body Heat

An essential guide to buying a wetsuit by Matt Crowther and Steve Warren.

Wetsuits are the most common thermal protection worn by divers. In water temperatures as cold as 10 or 12 degrees and within commonly accepted recreational depth and time limits, they perform well. Unlike drysuits, which offer protection at lower temperatures, wetsuits do not need to be equalised with compressed air to prevent suit squeeze. Minor punctures or tears are easily fixed and are not usually severe enough to stop a day’s diving. Wetsuits cost less to buy and maintain than drysuit systems. They are also usually lighter to take travelling.

They perform less well than drysuits as water temperature decreases and depth increases, as dive times are extended, or repetitive dives are made

How to avoid the big chill

Water is a powerful conductor of heat, drawing it away from the diver’s body. If body heat production cannot match the speed at which the water absorbs it, the diver eventually becomes chilled. This chilling affects both the ability to think clearly and impairs control of body functions like dexterity. Wetsuits act only to slow down heat loss – they cannot replace lost body heat. They do this in two ways. Firstly, the suit creates a physical barrier that body heat must cross in order to reach the cooler water outside. The thicker the suit, the longer this takes and the longer chilling is delayed. Secondly, they only allow a small quantity of water to make contact with your body. The more often water enters and exits the suit, the greater the amount of heat that is used from the diver’s body to warm it. To combat this, wetsuit designers try to ensure a close fit that sculpts around the diver’s body. Special features like seals and waterproof seams and zips may be used to decrease water flow. Water movement through the suit is called ‘flushing’.

Making your choice

Three factors should determine your choice of wetsuit: planned maximum depth, anticipated water temperature (it is usually cooler, the deeper you dive) and work rate. For example, instructors who spend long periods stationary while teaching entry-level courses and are acclimatised to the water temperature will often need a thicker wetsuit than a holiday diver. Acclimatisation occurs most obviously for a diver making the transition from cold to warm water diving.

They can allow you to get too warm

We need to remember that as important as it is to avoid getting cold during the dive, it is also important to avoid overheating both before and after. A hot and bothered diver is a familiar sight, and is usually the result of putting on exposure suits a long time before the dive itself. Dehydration is known to increase the body’s disposition to decompression sickness, as it significantly affects a diver’s ability to reduce bubble formation.

Comfort counts if you want to be safe

When buying a wetsuit, a diver must not only consider the correct choice for the environment but also its comfort and fit and its relationship to other equipment. An uncomfortable BC/wetsuit combination, for example, can draw a diver’s attention away from more important matters such as monitoring dive time and depth. When wearing thin warm-water suits especially, discomfort often occurs with a ‘hard pack’ BC. Additional features such as spine pads are worth looking out for.


Not everyone is a standard size

It is important to have a correct fit. If it is too loose the suit will be ineffective at minimising water flow. However, too tight and it will reduce your body’s blood flow. Both outcomes will result in rapid heat loss. A well-shaped wetsuit is essential to reducing flushing. It must closely follow the contours of the human body. A badly-shaped suit will have pockets of water in it. A combination of stretchier neoprenes, contoured shaping and a range of sizes means that many – but not all –people can be accommodated with off-the-peg suits. For those of a non-standard size, ‘made- to-measure’ suits are available from most but not all companies. It may take six or more weeks to deliver a made-to-measure suit. And the suit may need small final adjustments. It may be worth visiting the manufacturer for a fitting.

What to Look For


Expanded foam neoprene rubber is used to make wetsuits. Like an Aero bar, the neoprene is filled with bubbles. The nitrogen bubbles can be produced by a chemical reaction (chemically blown) or injected into the neoprene (gas blown). Gas blown is considered to be more consistent in its production qualities. It is usually more supple. The gas bubbles are poor conductors of heat. Small bubbles are preferred as they resist compression better than large bubbles. This further slows heat loss. Neoprene is available in thicknesses of 1mm to 8mm. Quoted thicknesses for suits are expected to be within 0.5mm. Neoprene is naturally stretchy when new but as the suit wears out it loses this property. With repeated use the neoprene bubbles break down, reducing the suit’s insulating powers and its buoyancy.


Thin, one or two millimetre neoprene vests are an option to keep core temperatures high. Be careful when layering with thicker neoprene. Restricted breathing, especially with increased workloads, can cause shortness of breath, produce carbon dioxide build-up in dead air spaces and induce panic.


Zips make putting your suit on and taking it off easier, at the expense of introducing breakage points and increased flushing. Most suits have entry zips in the front or back. Back zips follow the contours of the spine and are often easier to remove unaided than one-piece front-entry models. Zips placed in the forearms and calves allow the suit to be folded back on warm days to aid cooling. To prevent corrosion, metal zips of aluminium or brass or nylon or plastic-coated zips and teeth are used. Backing flaps help to minimise flushing.

A few suits incorporate drysuit zips to ensure water cannot escape through here.


Wetsuits are usually glued edge-to-edge and then stitched. Some suits are flat-locked, which means the edges are cut diagonally and laid over each other to make a more waterproof join. The main seams that hold the suit together are usually Mauser, Strobel or cup stitched. Mauser creates a flat stitch than can be more comfortable against the skin, but results in needle holes along the seam allowing in water. Strobel and cup stitches are waterproof and are also used on drysuits. The thread does not fully penetrate the suit. Cup and Strobel sewing machines are expensive to buy and as the suit must often be stitched twice, it is more labour intensive to produce – obviously reflected in the final price.


Usually suits are nylon-lined, making the suit easy to get on and off. The lining adds strength, minimising the risk of putting a thumb through the rubber, and provides a strong surface for the stitches. Externally the suit may be smoothskin, stippled or faced with nylon or Lycra. Smoothskin is a plain rubber finish. It minimises surface area, in turn slowing heat loss, and dries swiftly, inhibiting windchill. A stippled rubber facing, often called sharkskin, increases the surface area of the suit and is not so warm. It is more tear resistant than smoothskin. Nylon linings are slow to dry out of water, making wind chill a significant factor (a windcheater will help take the edge off this). They resist abrasion well and are hard to tear. Lycra linings are very stretchy and faster to dry than nylon. Both nylon and Lycra suits are easy to dry stitch from both sides. These suits are called double-lined.


Wetsuits with fitted wrist and ankle seals are known as semi-drys. Smoothskin cuffs help reduce water movement through the suit. Hoods often have a smoothskin seal around the face. Some suits have special seals designed to dock with dedicated gloves and boots.


Suits are available in a range of colours. Team colours can be used to identify leaders and students, or suit sizes in the rental locker. Spear fishermen, underwater film-makers and photographers all have a requirement to get close to marine life and may choose camouflaged suits. Models for photo shoots may choose high visibility complementary colours to enhance pictures. Some divers think that looking different to local prey species may reduce the risk of shark attack.


A snug fit around the torso is most important to slow down core body heat loss. Remember, most of the body’s vital organs are situated there.

Hoods, gloves and boots

Hoods that seal tightly can cause aural barotrauma. This happens when external pressure is not properly transmitted to the diver’s outer ear and is similar to wearing ear plugs. Care should be taken to flood the hood at the beginning of the dive. Hoods can be built in or separate. Zips that run up to the cheek can restrict head movement. Separate hoods sometimes have bibs which are meant to divert water over the top of the suit. If it is tucked into the jacket, cold water will be channelled into the jacket. Wearing exposure accessories such as gloves, boots and a hood helps to keep extremities warm and slow down overall cooling. Remember, around 75 per cent of total body heat can be lost through the top of your head.
Crucial kids’ stuff

Young divers need to take special care when selecting a suit system. Their build may require a made-to-measure fitting. Because they lack physical strength compared to an adult, getting a suit on and off may be more difficult and require more energy. Swimming in wetsuits requires energy to move in the restrictive material and may tire a youngster. It should be noted that children lose heat faster than adults due to their large surface area to mass ratio. Purchasing oversized suits to provide ‘growing room’ is also inadvisable, as is using hand-me-downs that may have lost much of their insulation.

Finding the right weight

It is important that individuals make an effort to correctly weight themselves before every dive in a new or unfamiliar suit. And, as the following results from a pool test reveal, it is not always easy to guess exactly what effect a different suit will have on your buoyancy. A two-piece clearly has a very significant positive effect, but few people would have guessed that the steamer was neutrally buoyant.

To further illustrate how easy it is is to make the wrong assumptions about weighting a suit, we asked four experienced divers to estimate what weights they would have thought necessary to achieve neutral buoyancy for the same suits. Given that everyone’s inherent buoyancy varies, this still reveals some serious discrepancies. Clearly the only way to get your weighting right is to do it in the water.

It is important to remember that all wetsuits will compress as you descend due to the surrounding water pressure, resulting in overweighting at depth. The closer you are to neutral buoyancy at the surface, the less overweight you will be during the dive.

© COPYRIGHT Dive International Publishing Ltd, for personal use only
About us | Disclaimer & terms of use | Contact us | Site News | Suggestions | Link to us | Advertising Info