Wetsuits and Heat Loss

Post by DPM Diving

September 25, 2021

Your body, in contact with water, can lose heat up to 30 times faster compared to air. This is the fundamental reason why divers use a thermal protection system. These include wetsuits, hoods, gloves and boots or booties.

In this post, you will learn about heat loss when diving and we will dive into the world of wetsuits.

Heat Loss

While air is an excellent insulator for blocking heat transfer, water is an excellent conductor. In other words, water absorbs heat from your body much faster than air. 

How Divers Lose Heat

Divers lose heat through two processes: conduction and convection. Conduction is the mechanism of heat transfer through matter by molecular activity, by the collision of some molecules with others, where the more energetic particles give energy to the less energetic ones, producing a heat flow from higher to lower temperatures. 

Let us illustrate this concept with a diving situation. The human body has an average temperature of between 36.5 and 37 degrees Celsius. Imagine that we dive without any thermal protection and the water temperature is 26 degrees. The heat flow will be from our body to the surrounding water molecules. That is to say, our body will lose heat until it reaches an equilibrium with the surrounding medium. 

In addition to losing heat by conduction through contact with water, our body also loses heat by internal conduction. This happens when we breathe the air in our tanks. Scuba tanks contain compressed air. When the air leaves the tank and loses pressure, it cools down. In these circumstances, our body uses internal heat to warm the air we breathe.

Convection is the mechanism of heat transfer by mass movement or circulation within the substance. In other words, in a diving scenario, water molecules that are in contact with our body are heated and then replaced by cooler molecules.  Hot water is less dense than cold water and therefore rises, causing convection currents that transport energy.

Factors Affecting Heat Loss

Cold does not affect everyone the same way, both in and out of the water. In addition to how sensitive you are to the cold, there are a number of factors that have a great influence on your diving:

  • Previous dives: When we make successive dives during the same day, we lose heat faster. This is because your body has not had time to fully recover its body temperature. 
  • Dive duration: the more time you spend underwater, the colder you will be. Keep in mind that during this time your body is “fighting” against the cold by using its reserves. If you are cold, it is advisable to make shorter dives.
  • Physical effort during diving: The more you exercise underwater, the more heat your body will generate and the less cold you will feel, just like out of the water. But be careful, this sensation will only be momentary and only for environments where the water is at least 24 degrees. In colder water and without the proper equipment, you will lose heat much faster than if you stay in a static position. If you already feel cold and start moving to counteract it, it will be worse. Blood circulation through the muscles of the body, immersed in a cold environment, causes the inside of the body to cool down faster.


According to DAN Alert Network, Hypothermia occurs when the body loses heat faster than it can produce it. Normal body temperature hovers around 37 C, and hypothermia occurs as that temperature dips below 35 C. As the body gets colder, it becomes harder for organs to function properly. When left untreated, hypothermia can lead to heart and respiratory system failures.

Common symptoms of hypothermia include weakened pulse, confusion, slow breathing, shivering, and even loss of consciousness. Cases of hypothermia vary from mild to severe.

A mildly hypothermic person may be shivering and conversing lucidly. A severely hypothermic person may be unconscious and have a very low heart rate.

Hypothermia is not limited to colder conditions; it can even occur in tropical waters. Regardless of whether you’re diving in colder temps or tropical climates, the best way to handle hypothermia is to plan for it and prevent it. The right diving suit will certainly help protect against hypothermia.

Diving Wetsuits

In order to dive comfortably and safely, we must prevent or delay the loss of body heat so that we can enjoy diving without running the risk of hypothermia. As mentioned above, one of the most important components of the thermal protection system is the wetsuit.

  • drysuit - Wetsuits and Heat Loss
  • semy dry - Wetsuits and Heat Loss
  • wet suit - Wetsuits and Heat Loss

Type of diving suits

There are three types of suits:

  • Dry
  • Semi-dry
  • Wet

Divers choose their suits based on water temperature. While this choice varies from diver to diver, there are certain “limit” water temperatures where each particular suit is recommended.

Dry Suit

The drysuit is used in very very cold waters, in dives in waters below 16ºC. The drysuit, as its name suggests, keeps the diver dry at all times and avoids contact with water. 

Due to the presence of air inside, these suits greatly affect buoyancy. Therefore, in order to be able to adjust it, it is necessary a series of valves that allow the inflation and deflation of the suit.

There is usually one on the chest that connects with a hose to the regulator to inflate it and another on the left arm that allows deflation.

The use of a drysuit is an added difficulty in buoyancy control. Therefore, to dive with a dry suit it is necessary to take a specific course, in which you learn how to use it correctly and prevent possible problems.

Semy-dry Suits

Semi-dry suits are thick (5 to 7 millimeters) neoprene suits that allow a thin layer of water to enter and heat up on contact with the body. In these types of suits, the sleeve and ankle cuffs are tight-fitting and the closures are watertight. Although not designed to completely block water entry as in a drysuit, these zippers minimize the amount of water that can access the interior of the suit.

Wet Suits

Finally, wet suits are suitable for diving in tropical and subtropical waters. As the name suggests, when we dive with this type of suit we still get wet. However, these suits help us lose heat more slowly as the thin layer of water trapped in our suit warms up, insulating us from the surrounding colder water. Unlike semi-dry suits, these suits are thinner and do not have watertight closures or tight arm and leg cuffs. 

Not only prevents heat loss

Although the main function of a wetsuit is to provide thermal protection, these suits are also used to protect us from the sun, to prevent the diving equipment from rubbing against the body and to prevent possible injuries due to unwanted contact with the surrounding environment.

Wetsuits, like semi-dry suits, are made of evenly blown neoprene cells made of air or nitrogen gas in closed cells. The neoprene is lined with fabric or foam that adds strength and color, and also makes it easier to slide inside. These suits can vary in thickness (the thicker, the more insulating), length of arms and legs, and particular features of the model (zippers, reinforcements, etc). 

Among the most popular, we find the 5 millimeters (mm) long suits and the 3mm suits that can be long or short. The latter, being thinner, do not have as high thermal protection as the 5mm suits, but are very flexible and comfortable to put on and take off. They are ideal for very hot tropical environments, since in the boat we will not suffer as much heat exposed to the sun as with thicker suits.

It is important to note that while these two thicknesses are the most popular among wetsuits, they can vary from 7mm to as little as 1mm, or even have a combination of thicknesses.  For example, in a “2-3” shorty suit the chest will be made of 3mm neoprene and the rest of the suit will be 2mm.  


To conclude, keep in mind that in order for wetsuits to protect you from heat loss, they should fit snugly to the body, avoiding wrinkles or baggy spaces on your chest and back. 

We hope you are now more familiar with thermal protection systems and feel better prepared for your next dives. Stay tuned for new posts on this and other diving related topics.

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