Why We Have Different Products for Humid Heat vs Dry Heat

A long-sleeved shirt can actually feel good in the dry heat of the desert, but the same covering in sticky, humid heat can be awful. Why? Evaporation (or lack there of).

I’m a California guy at heart. I say “the” 405 or “the” 10 (grammatically, I insist that this is correct). My cortisol spikes when someone claims Whataburger is better than In N Out. And I will absolutely insist that dry heat is more tolerable than humidity. People from the Northeast or South complain when they come to SoCal or Arizona about them needing to moisturize more. Big deal - better than sweating profusely and not being able to find relief in the shade.

It feels different because our body has to cool ourselves in different ways. In general, when it’s hot, your body tries to cool down by sweating. Sweat works when it turns into vapor, but if it can't evaporate, it just sits on your skin, soaks into your clothes, and makes you feel damp, stuck, and increasingly uncomfortable.

This single fact completely changed how we approached designing for hot weather.

Some friends of the brand know that I initially didn’t want to design short-sleeved shirts. I prioritized UV protection and coverage. But my co-founder, who is born & raised in the northeast, convinced me how humidity is a whole different animal (as with many things, he was right and I was wrong). The same long sleeves in the humidity were now trapping the moisture that just wanted to escape from the arm holes.

So through two grueling summers of testing & prototyping, we established that dry and humid heat demand different solutions, so we designed different products.

Our Canyonlands long sleeve button up and White Sands hooded henley are for drier climates. In those places, protection from the sun and its UV rays is hugely important, and there's plenty of opportunity for sweat to evaporate.

The Everglades short-sleeve button up and (upcoming) Congaree short-sleeve henley, however, are for humid conditions. Both are for hot weather, but they tackle different hot-weather issues.

Dry Heat and the Benefits of Covering Up

In dry heat, long sleeves actually are better for you. It might seem unintuitive, but hear me out.

Yes, bare skin immediately feels the air, which can be nice for a moment. But bare skin also gets the full blast of the sun's heat and UV rays. In a wide-open desert, on light-colored rock, sand, hardpan, pavement, or by a river, the sun isn't just bright, it’s a heavy load of energy.

Protective, long-sleeve clothing changes that.

A loose long-sleeve shades your skin, lowers your exposure to UV rays and prevents the sun from directly hitting all of your arm. And, if the fabric isn't stuck to your body and the air is dry, sweat and moisture can evaporate both through and around the shirt.

This is why a long sleeve can be surprisingly comfortable in places like southern Utah, West Texas, New Mexico, Arizona, or in Death Valley type heat. Death Valley National Park calls itself the hottest and driest place in North America; summer shade temperatures often go above 120°F, and they get less than two inches of rain a year.

These are extreme conditions, and a shirt alone won't make them safe - you also need to be aware of the time of day, find shade, drink water, eat, and use good judgment.

But in dry heat, evaporation can happen. A long-sleeve made with a lot of hemp can hold a little sweat or water and then release it slowly as the air flows over the fabric. What might seem like a disadvantage in a situation where you're trying to "stay dry" can actually be useful in a dry, hot climate.

The aim isn't to get dry as quickly as possible.

The aim is to balance sun protection, moisture, and airflow.

Humid Heat and Trapped Moisture

Humid heat gets stickier.

In places like the Everglades, Congaree, or even urban areas like DC or NYC in the summer, the air is already highly saturated and so the moisture from your body isn’t able to evaporate as quickly into the ambient surroundings.

That's a completely different problem than the dry desert heat.

In the humidity, a shirt can get wet and stay wet. The tiny area between your skin and your clothes can become a warm, soaked little environment (like your personal little Equinox spa that you wear). More coverage can mean more fabric holding moisture against you.

That's why the same long-sleeve that feels good and protective in dry heat can feel suffocating in humid heat.

It’s not that long-sleeves are fundamentally bad. As I wrote earlier, they’re actually better in the dry heat. But in humid heat, evaporation is slowed to a crawl. You now need to focus on reducing how much fabric is against your skin, opening up the clothing, increasing airflow, and giving moisture fewer places to be held.

That’s the reason for the Everglades short-sleeve button-up and the upcoming Congaree short sleeve henley. Short-sleeves don't cover your arms as much as long sleeves - and that’s a trade off. You might need more sunscreen. You might want a hat, sunglasses, or separate sun sleeves sometimes. And in buggy areas, you might still prefer more coverage.

But when humidity is the biggest issue, less fabric can feel better because there’s less wet material stuck to you, less soaked surface, and a better chance for air to get to your skin.

Why we split the line

It would be tempting to follow the line of other DTC “marketing bros” and loudly shout in your face, “You’ll never need to wear ANY shirt every again” or “this is the ONE shirt you’ll ever need.”

And guess what? That would’ve been dishonest, and not helpful nor respectful to you.

We’ve designed our clothing to deal with the specific difficulties of each climate.

The Canyonlands long-sleeve button up and White Sands hooded henley are all about shielding you from the sun, blocking UV rays, and keeping you comfortable in dry heat. They’re for days when the sun is intense, and because the air is so dry, sweat can evaporate and cool you down.

The Everglades short-sleeve button up and the Congaree short-sleeve henley focus on cooling you in humid weather. They have less fabric, allow air to move more easily, and don't hold moisture against your skin. They are for when the air is already wet and you really need to get air circulating. The compromise is you won't get as much sun protection as with the long sleeved options.

How to pick

Start by thinking about the humidity, not just the temperature.

If it’s hot, sunny, dry, and you’re in the open, long sleeves could be a good idea. If sun protection is the most important thing, if you won't have much shade, and if sweat can evaporate, the Canyonlands or White Sands style is the way to go. You can even get the fabric wet on purpose if you have water and the dryness means it will evaporate and cool you down.

If it's hot, muggy, still, and you can feel sweat sticking to your skin, go for the Everglades or Congaree. This is especially common in the South and the East Coast, or the high desert regions if it's the middle of monsoon season. Let the shirt be breathable, open the neck, and allow for more airflow to your arms. Be aware that you might need to use sunscreen or another method of sun protection because the clothing won't cover as much.

Even in humid conditions, if bugs, bushes, or really strong sun are more of a problem, more coverage might still be best. Also, if the heat is dangerously high, neither long sleeves nor short sleeves will solve the overall problem of safety. Start out earlier, don't go as far, find shade, and slow your pace.

Unfortunately, as with many things in life, good solutions still have trade-offs, so it's best to just be aware of these things in advance. 

If you have any other questions, please feel free to let us know. Write to me at doug@terlinguathreads.com, and I’ll try to answer any questions to the best of my abilities.