Exposure protection
0 of 4 hands-on
01 Introduction
Warm divers are comfortable, alert and safer. Water pulls heat from your body far faster than air does, so almost every diver wears some protection. This lesson explains how suits work and how to choose one.
Objectives
- Explain how divers lose heat in water and why exposure suits matter
- Compare wetsuits, semi-dry suits and drysuits
- Choose a sensible thickness for the water temperature, and recognise cold stress
02 Watch
Keeping the heat in
4 min · Video in production
- 1
A thermal image of a diver in cold water, with the heat visibly leaving the head and body.
- 2
A cutaway of neoprene showing the tiny gas bubbles that trap heat.
- 3
A wetsuit with a thin layer of water between the suit and the skin warming up.
- 4
A drysuit being sealed at the neck and wrists, with a diver staying dry in cold water.
03 Learn
Why divers get cold
Water conducts heat away from the body about 25 times faster than air at the same temperature. A diver in water that feels pleasant for swimming can still lose a great deal of heat over a long dive. The body also loses heat as it warms the gas that is breathed in from the cylinder. A diver who gets cold becomes tired, makes mistakes and uses more gas.
Wetsuits
A wetsuit is made of neoprene, a foam full of tiny gas bubbles that insulate. It lets a thin layer of water in. The body warms that layer, and the suit helps to keep it from being flushed away. A good fit matters more than almost anything: a suit that is too loose lets cold water flow in and out.
Take a guess first
If water removes heat about 25 times faster than air, how many times more heat would a diver lose in the water than in air of the same temperature after the same time, as a rough guide?
How thick?
The right thickness depends on the water temperature, the length of the dive and the diver, because people feel cold differently. This table is a rough starting guide only.
| Water temperature | Typical protection |
|---|---|
| Above about 28 degrees Celsius | Swimsuit or thin rash vest, or a very thin suit |
| About 24 to 28 degrees Celsius | 3 mm shorty or full suit |
| About 18 to 24 degrees Celsius | 5 mm full wetsuit, sometimes with a hooded vest |
| About 10 to 18 degrees Celsius | 7 mm wetsuit with hood, gloves and boots, or a drysuit |
| Below about 10 degrees Celsius | Usually a drysuit with thermal undergarments |
Neoprene compresses with depth and loses some of its insulation. A suit that is comfortable at the surface will feel thinner at 30 metres. Dives that are long, repeated or deep make heat loss more important.
Semi-dry suits and drysuits
| Type | How it works | Notes |
|---|---|---|
| Semi-dry | A thick wetsuit with seals at the wrists, ankles and neck that limit water flow | Warmer than a standard wetsuit of the same thickness |
| Drysuit | A waterproof suit that keeps the diver dry, with warm undergarments inside | Excellent in cold water, but it adds gas to manage, and needs specific training |
Hoods, gloves and boots
A large amount of heat can be lost through the head, hands and feet. In cooler water, a hood, gloves and boots make a big difference. Gloves can protect the hands from cuts, and in some marine parks they are not allowed because they encourage touching. Check the local rules.
Predict first
You are shivering at the end of a long dive. What is the right response?
Cold stress
Signs of becoming too cold include shivering, numbness, poor coordination, trouble thinking clearly and, in serious cases, confusion. A diver who feels cold should end the dive. After diving, get warm gradually and drink warm fluids. Hot showers can feel good but should be used with care if you are very cold.
04 Explore
Try it yourself
Match each suit type with its description.
Match each suit type with its description.
- Wetsuit
- Semi-dry suit
- Drysuit
- Hood
- Neoprene compression
05 Apply
Scenario
You are planning to dive in 20 degree Celsius water, on three dives in a day. The dive guide says that a 3 mm shorty would be fine. You get cold easily, and you plan to dive for around an hour each time.
What is the sensible choice?
06 Check
07 Summary
Key points
- Water takes heat from the body about 25 times faster than air.
- Wetsuits trap warmed water. Fit matters, and thickness depends on water temperature, dive length and the diver.
- Neoprene compresses at depth. Semi-dry suits reduce flushing and drysuits keep you dry but need training.
- Hoods, gloves and boots help in cooler water. Shivering is a reason to end the dive.
Before you apply this in the water
- Have I been trained by a qualified instructor for this?
- Am I medically fit to dive?
- Do I have a buddy and a plan?
- Am I diving within my training and limits?
Answer every question in the Check section to mark this lesson complete.