How Does a Wetsuit Keep You Warm?

repairing wetsuit

Wetsuits are insulating pieces of water equipment that covers most of the body (from neck to ankles and wrists) or in parts such as vests and shorts. Just like cold-weather clothing, wetsuits are designed to keep your natural’s body heat from escaping and to protect against abrasive hazards like sharp rocks and coral.

Thanks to its neoprene material, skin tight fit, and water-resistant construction, the cold water that enters the wetsuit will quickly get warmed up by your trapped body heat. Instead of feeling like you’re swimming in cold water, it’ll feel like you have a constant layer of warm water protecting your body from the cold. That’s a highly simplified explanation of how wetsuits keep you warm.

In this article, we’ll go over the science behind how wetsuits work, the intricacies of their design, and various ways you can select the best wetsuit to keep you warm.

How does a wetsuit keep you warm in cold water?

Most wetsuits are constructed by combining neoprene rubber laminated to nylon, spandex, polyester, or a similar fabric. The benefit of this is the material can stretch for a snug fit as well as give you the range of motion to move your body without compromising the quality of the suit.

Wearing a wetsuit is like putting on a second, thicker layer of skin that can protect you from the cold and other, more physical hazards such as jellyfish stings and coral. Specifically, this “second-skin” is waterproof and has thousands of air bubbles trapped inside it that prevents heat from escaping.

Though we tend to think of the wetsuit as an entire layer on its own, actually it is composed of three to four layers and each has a different purpose:

  • Comfort (inner) layer. This is the innermost layer that will have contact against your skin. It is designed to be softer and smoother to discourage chafing and promote comfort.
  • Heat-reflecting layer. This layer is made of some kind of heat-reflecting material that prevents body heat from passing through it. It does a similar job to the neoprene layer. Not all wetsuits will have this layer.
  • Neoprene layer. This layer comprises the bulk of the wetsuit construction and will have varying elasticity and thicknesses (3mm to 6mm+). The bubbles trapped inside neoprene are excellent insulators and also make the wetsuit positively buoyant. Hypoallergenic wetsuits do not have any neoprene because it can sometimes cause allergic reactions in individuals.
  • Outer layer. This layer is made of durable and resilient material that protects the wetsuit from wear and tear.

The more layers your wetsuit has, the greater the insulation it will provide. This is because each layer traps warm air between them, and actually it is this air that keeps you warm, not the warm water. It’s also why wearing a base layer under the wetsuit can be so effective at keeping you warm, because it is yet another layer. Conversely, this also means that if you only have one layer, no matter how thick it is, air will more easily find its way out.

A snug fit

what to wear under a wetsuit males and females

In order for a wetsuit to be effective, it needs to fit snug on your body. It should not be so constrictive that you cannot move, struggle to breathe, or disrupt your blood flow, of course. However, it does need to lightly press against your skin to provide effective insulation from the cold.

As we mentioned, some water will enter your wetsuit so don’t be alarmed when it happens. Despite being soaked, there should only be a thin layer of water between the suit and your body. Your body heat will be trapped inside, warming up the water as well. In a high-quality wetsuit, the warm water will mostly be trapped with very little cold water entering and warm water leaking out.

Conversely, in a baggy or low-quality wetsuit, cold water will constantly rush in and flush out any warm water. The cold water will make contact with your skin and steal your precious body heat away. You will constantly feel cold if the wetsuit doesn’t fit you snug enough which defeats the purpose of even wearing it.

For this reason, you need to find a snug wetsuit because it will be much more effective at keeping you warm than a baggy one.

Heat retention

Why is it so important to retain your body heat in the water? Water is about 25 times more effective than air at taking heat away from your body due to its higher density and heat capacity. According to physics’ second law of thermodynamics (i.e. the science of heat transfer), heat will flow from a hotter object to cold objects nearby.

Take for example, your own internal body temperature of 36°C. When you expose yourself to cool air that is 15°C, your temperature will drop as the heat moves into the air, and you will experience this as a chilly wind. When your body is in a body of water, even “warm” water, the result is that your core temperature will be rapidly cooled since water is so much more effective than air at transferring heat.

This is the same reason why you could spend an hour on a hot sunny day swimming or snorkeling, and come out of the water shivering with blue lips. The entire time you were in the warm water, it was bringing your body’s temperature closer to the water’s temperature which can cause hypothermia in the human body.

To combat this, wetsuits are made up of many layers that trap your body heat. Each layer acts as a type of “airlock” that the air tries to flow through. Since air is mostly empty space, each layer makes it harder for the air to pass through, and this is known as insulation. With the hot air trapped inside and so close to your body, you will stay warm.

Without a wetsuit, the water molecules will draw the energy, or heat, from your body faster than your body can replenish it. Even in warm waters, if you plan on spending a long time in it, you should consider wearing some kind of protection.

Wetsuit thickness and temperatures to wear them at

Water Temperature Range Wetsuit Thickness Recommended Wetsuit Type Seal Type
>72°F (>22°C) N/A Rash guard N/A
65°- 75°F (18° – 24°C) 0.5 mm – 2/1 mm Top / Shorty N/A
62°- 68°F (16° – 20°C) 2 mm – 3/2 mm Springsuit / Full Suit Flatlock
58°- 63°F (14° – 17°C) 3/2 mm – 4/3 mm Full Suit + Boots Sealed
52°- 58°F (11° – 14°C) 4/3 mm – 5/4/3 mm Full Suit + Boots + Gloves + Hood Sealed and Taped
43°- 52°F (6° – 11°C) 5/4 mm – 5/4/3 mm Full Suit + Boots + Gloves + Hood Sealed and Taped
42°F (6°C)  and below 6/5 mm + Full Suit + Boots + Gloves + Hood Sealed and Taped

Stitching

wetsuit fit

If you’re not aware, wetsuits are actually constructed from various pieces that are stitched together to form one large piece. Everywhere there is a stitch is a small hole that water can seep in from. Water is tricky to deal with because even the tiniest of spaces can cause a leak. The more water that can enter the suit, the less effective it will be at keeping you warm.

Wetsuit manufacturers are aware of this problem, of course, so they have various stitching methods to keep water seepage to a minimum. Water should only be entering from the neck, ankle, and wrist openings. The wetsuit seams are typically made using the flatlock or blind stitch method. These two styles provide different levels of water sealing capability.

With the flatlock type of stitching, a needle will go through both ends of the fabric in order for the thread to pass through. No matter how tightly-knit it is, water will find its way through because of the top-to-bottom holes that the needle opened up. For summer wetsuits, this type of stitching is suitable since temperature control is less of a concern.

Blind stitching is a more waterproof way of knitting two pieces of cloth together. The two pieces of fabric are glued together. Then, the needle and thread are used to bind the pieces together. The wetsuit will be sewn in such a way that the needle doesn’t actually pierce all the way through to the other end of the fabric.

The manufacturer may even tape tape over the seams for yet another layer of water protection. Wetsuits made this way are effective at preventing water seepage and will keep your body warm in the water.

Zippers

We’ve already mentioned how water can enter from the ankle, wrist and neck opening and flush out the warm water inside. However, water can also enter from the seams and zipper. In a high-quality wetsuit, even these are minimized or outright prevented.

For instance, some wetsuits have dry-zips (just like those found on drysuits) instead of a regular zipper. This prevents any water ingress, however this can also double the cost of a wetsuit. In our opinion, the cost is not justified for the little benefit it provides. If you care very deeply about staying warm, however, then it is something to consider.

A budget way to prevent water ingression through the zip is by including a zip baffle (or a “batwing”) which is an extra piece of material that follows behind the zipper and blocks any water from going past it.

Be wary of evaporative cooling

The traditional wetsuit design is effective for heat retention while underwater, however above water there is an evaporative cooling effect. When performing water surface activities such as surfing or kiteboarding, the wind will blow away the layer of water directly above the wetsuit, taking away the heat accumulated. This is known as evaporative cooling, and as your suit builds up another water layer, it will also be lost to the wind.

To show this in effect, you can do a very quick test right now. First, blow against the back of your hand. That probably didn’t feel very cold, did it? Now wet your hand and try blowing again. It should feel significantly colder. Even with the protective layer of a wetsuit, you can still feel cold above water with a wetsuit due to evaporative cooling.

In order to prevent this, you can wear a smoothskin neoprene wetsuit. The smooth surface of this type of wetsuit causes water to easily slide off, thereby reducing the effect of evaporative cooling. While this solution does work, it may not be necessary.

If your water sport activity is diving, you will spend most of your time underwater where there is no evaporative cooling. Even for an above water sport like surfing, surfers will spend most of their time underwater as they wait for a good wave. Even other above water sports like sailing, kayaking, and water skiing require one to wear a buoyancy aid which offers some protection against evaporative cooling.

Finally, evaporative cooling will occur whether you wear a wetsuit or not. Even a wet wetsuit on the surface will offer you some insulation against the cold-amplifying effects of evaporative cooling. The concept of evaporative cooling is something to keep in mind, however in many situations it’s not a problem.

Emergency warmth

There is a technique which we hesitate to recommend, though it can be handy in an emergency. Many people lament the fact that swimmers like to urinate in the pool, and the same is true for the ocean as well. When you’re in a wetsuit and you don’t have easy access to the bathroom, then when you gotta go, you gotta go.

In a pinch, weeing in your wetsuit (known affectionately as a “wetsuit warmer”) can temporarily provide some much needed warmth. The urine is the same temperature as your body so it’s already going to be a comfortable temperature. The thought of swimming in your own urine seems disgusting, but keep in mind, water is constantly being replaced in your wetsuit. Eventually, all of the wee will be washed out and replaced with ocean water.

If you are shivering and need a temporary reprieve from the cold, consider using a “wetsuit warmer.”

Parting words

To sum it all up, wetsuits can keep you warm by trapping your body heat and keeping it close to your skin. Water will enter your wetsuit, get warmed up, and add another layer of insulation inside the suit. The goal is to keep as much water out as possible so that the warm water inside is not immediately flushed out, and your body temperature can remain high.

There are various considerations to keep in mind when purchasing a wetsuit. It is completely useless if it does not have a snug fit on your body. It should also be an appropriate thickness for the water temperature you will be wearing it in. Depending on the stitching method used, flatlock or blind-stitched, water may seep in through the seams as well as zipper.

In addition to keeping you warm, wetsuits add an extra layer of protection against cuts, scrapes, and marine life such as jellyfish. Whether you’re a surfer, snorkeler, or SCUBA diver, you can surely benefit from wearing a wetsuit if you’ll be spending a lot of time in the water.