What If I'm Wearing a Wetsuit or Drysuit In Hot Weather?

There are no exceptions to the rule “Always Dress For The Water Temperature”, and it's a dangerous mistake to skip wearing a wetsuit or drysuit when the water is cold but the air is hot.

 

Your Key To Safety and Comfort:

Get your clothing or the surface of your wetsuit or drysuit wet. Wet your hair, and wear a wet hat, wet bandana, or anything else that will allow you to offload heat via evaporation. Note: You can still use evaporation to keep cool when the humidity is high.

 

Fabrics differ in how efficiently they absorb water. My old wetsuit absorbs enough water to provide evaporative cooling for 20 – 30 minutes. However, a lot of the newer neo sheds water and won't work for evaporative cooling unless you wear a wet shirt over the top of it. Same holds true for some drysuit fabrics. BTW: Moving air increases the efficiency of evaporation and high humidity retards it. 

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A Dynamic Process

I want to emphasize that this is a dynamic process. You have to work with it to maximize both conduction and evaporation and that takes some practice. However, it's well worth the effort, because paddlers who take advantage of these techniques don't have a problem with overheating while wearing thermal protection in warm or hot weather.

 

 

An Extreme Example - 14mm of Neo

Before I moved to Vancouver, WA, I paddled in the Chesapeake Bay area of Virginia and Maryland, where it wasn't unusual to have summer days with 80F+ water and 90F+ air with high humidity. I occasionally demonstrated the power of evaporative cooling to my students by wearing my two-piece wetsuit in August – a 7mm farmer john under a 7mm long-sleeved shorty. That's 14mm of neo over my core, and I topped it off with a neoprene balaclava hood. As long as I kept the neoprene wet, I was fine. If the neoprene had remained dry, I would likely have had a fatal heat stroke in under 30 minutes. That's the power of evaporation!

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What About Cotton?

When I posted this article on several Facebook paddling groups, I received a lot of pushback from people who questioned why I recommended cotton clothing for paddling. They argued that it was dangerous to wear cotton and they repeated the “cotton is rotten” mantra as if it applied to hot weather. It doesn't.

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In wilderness travel, all the warnings about cotton apply to cold weather situations where the challenge is keeping warm.

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However, this article is about keeping cool, not about keeping warm. It's about avoiding overheating by using evaporative cooling. It applies to hot days with full sunlight when you're paddling on warm water, and also to hot days when you're paddling on cold water and wearing thermal protection like a wetsuit or drysuit.​

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If your goal is to avoid heat stress, then cotton is a superior fabric because it holds more water and doesn't have to be re-wetted as often as synthetics.​ Although you shouldn't wear cotton under your drysuit, you can definitely wear cotton over your wetsuit or drysuit if you need additional evaporative cooling.

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Note: If your goal is keeping warm and avoiding cold stress, then cotton should be avoided because cotton fibers soak up water like a sponge, offer zero insulation when wet, and take much longer to dry than synthetics. For example, wearing cotton and getting caught without raingear in a 50F rainstorm on a mountain trail is an invitation to hypothermia.  This is why we warn against using cotton as a cold weather fabric.

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What About Dehydration?

The primary cause of dehydration is failure to drink enough water to replace fluid loss. A healthy person exercising in the outdoors loses fluid in two main ways: perspiration and respiration. Of these, perspiration (sweating) is the primary route. However, fluid loss via respiration can be significant in certain activities like high-altitude mountaineering as the result of cold, dry air and an increase in breathing rate.

 

Sweating is the body's natural response to a hot environment. Here's how it works: Fluid is excreted onto the skin, and as that fluid evaporates, it removes heat. That's all there is to it. It's a simple and very efficient process, particularly when humidity is low. Sweating becomes less efficient in high humidity because humidity interferes with evaporation. This is why people in hot, very humid environments can have sweat running down their faces and soaking into their clothing. They're sweating faster than evaporation can handle.

 

On the other hand, if you can keep yourself cool without sweating, you won't be losing a lot of water that needs to be replaced. That means you don't have to constantly drink a lot of water in order to avoid dehydration. This is precisely why using wet clothes to offload excess heat by evaporation is such a useful technique. BTW - You wouldn't know any of this from reading all the advice that recommends guzzling water when paddling in hot weather.

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Drinking Too Much Water

Taking this one step further, lets look at the rarely-mentioned downside of guzzling water while you're paddling. Drinking more water than necessary can leave you feeling listless, bloated, and nauseous. It can also require you to take frequent “pee breaks” to get rid of all that excess water. When taken to extremes, it can also lead to a medical condition called hyponatremia. In fact, in healthy people, the main cause of hyponatremia is drinking too much water.

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How can you tell if you're dehydrated?  A good rule of thumb is to check the color of your urine when you pee.  If it's clear or pale yellow, you're hydrated; if it's dark yellow or brownish in color, you're dehydrated.​

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Heat-Related Medical Problems - Prevention vs Treatment

People writing about outdoor safety often fail to distinguish between prevention and treatment. That's a big mistake. Prevention is all about learning how to avoid problems, but treatment only comes into play once the problem has occurred.

 

For example, whether you're hiking on a trail, paddling on the water, or working outdoors in hot weather, prevention is teaching people how to be safe and comfortable regardless of the heat. Treatment is dealing with heat-related medical problems like hyponatremia, heat cramps, heat exhaustion, and heat stroke.

 

If you review articles and videos about hot weather safety, you'll find that the focus is almost exclusively on treatment. They'll mention acclimatization, and give impractical "tips" like avoiding direct sunlight and resting in the shade - and they always emphasize guzzling water. But what you'll almost never find is any mention of the most effective way of preventing heat illness – which is using wet clothing and evaporation to reduce or eliminate heat stress.

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Although there's nothing wrong with teaching people how to recognize heat-related medical problems, doing so without mentioning prevention actually undermines safety.  Because from a safety standpoint, it's always preferable - and far easier - to prevent a problem from happening in the first place.

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Early Warning Sign

If you feel hot and uncomfortable and find yourself sweating, it's an early warning sign of heat stress, and you should take it very seriously.  It's especially easy to avoid heat stress when paddling - because you're surrounded by water. But no matter what activity you're doing in hot weather, you should look for ways to use evaporation to keep your cool in the heat.

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Bottom Line​​​​

• When you wet your clothes on a hot day, they will generally dry out in under 20 minutes. You are in complete control of the re-wetting process. When you have plenty of access to water, this is the most effective way to use clothing to regulate your personal comfort.

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• This technique allows you to use your clothes as your thermostat.  You control the set-point by deciding when to add water and how much water to add. With a little practice, you can dial in comfort and paddle on a hot day in full sunlight – while feeling like it's 75F outside. As an additional bonus, you'll avoid the need to guzzle fluids to replace those that you lose by sweating.​​​​​​​​​​​​​