Is cotton best in hot weather?

[Justin Baker]

In consistently hot weather, do you guys wear cotton or synthetics? I have always worn cotton, especially when I worked landscaping in 100+ degree weather. I don't have much experience with synthetic base layers, so I was wondering your opinions.

[Eugene Smith]

I wear cotton predominately for continuous dry heat activity, in excess of ~90F. They're even comfortable for me during the mid summer heat for running…. but this isn't accepted by many.

Synthetic shirts, even thin stuff like Capilene 1 T-shirts just get too stifling under direct sunlight in those temperatures, with the exception of Capilene 2 which works well if you're on the move and pushing out a lot of sweat or if there is a breeze.

I prefer threadbare cotton shirts or cheap 50/50 T-shirts that dry quickly in really hot conditions. Lightweight merino blends, of the lightest variety, are good around 90F still in dry heat conditions.

[Franco Darioli]

Some (like me…) adhere to the idea that the faster your clothing dries (in hot weather) , the more you will sweat because you produce sweat to cool yourself down.
The more you sweat, the more water you need to carry.
So I use wool (140 -190) in the bush and cotton at home. The new RAB MeCo looks interesting but other brands, like Macpac also have blands.
Franco

[Backpack Jack]

I have a lawn bussiness on the weekends, apart from my 9-6 job Mon.-Fri. I use to wear cotton shirts all the time, but switched over to the Capilene 1 T-shirts 2 years ago and love them. Where I live it gets into the 100 plus days for about 3 weeks straight, the rest of the time is high 90's with the humidity each year going up, its been around 50-65% the last couple of years. If the sun gets to hot, beating down on me I will put on my long sleeve Capilene 1 over my short sleeve Capilene 1 this has worked very well for me, especially if there is no wind out, I also wear a Kavu hat(looks like a Chinese rice hat, but newer material, not straw) and that helps keep my head and shoulders shaded. Hope this helps.

Jack

[Nick Gatel]

I suppose it depends upon your physiology. I wear Rail Rider shirts most of the time or a cotton poly blend. But then I don't know if you would consider 120F (48.9C) hot :)

[Eric Lundquist]

Growing up I would normally wear an old cotton t-shirt while hiking. My first few Boundary Waters trips were with t-shirts as well. I think that in the right conditions, it's the right garment for the job.

For me, they've gone by the wayside in preference for wool. I only carry one baselayer which I also sleep in at night so I need it to dry quickly. If you're in hot and dry conditions and prefer carrying a different camp shirt then I would say that cotton still works for you.

[David Thomas]

Jumping to the obvious: light colors are better than dark colors. It's easy to find a old white button-down shirt at Goodwill for $3.95 and use it on 100+F hikes. Whereas a lot of synthetic are dark colors. But if they are both in light colors:

I like a hot weather shirt to be light-colored (duh!), and loose. Loose so the heat of the sun happens AWAY from my body. Yes, some of the evaporation of sweat occurs away from my body, but which is greater – sweat or sun? It varies from uphill to down hill and hillside to hillside.

If everything is light, then cotton offers:

pros: holds water and cools when against your skin. Can carry additional water as you cross a creek or water source. For me, this is big – water I didn't sweat myself isn't as exhausting as water I did sweat out.

cons: if the weather or your exertion changes, that sweat-soaked cotton shirt can suddenly chill you. If the weather changes a lot and you need some insulation, the cotton gives you nothing if wet.

Whereas synthetics:

Pros: typically cling to your body so your sweat evaporates right next to your skin where it helps you the most. Is it still useful clothing if wet or if the weather later demands some insulation.

Cons: solar input to the fabric also is released next to your skin. They can't carry much creek water to help cool you from the outside.

My choices:

Totally hot and dry hike (GCNP in June-July-August): cotton dress shirt in a light color.

Overnight with hot days, cool nights: light-colored synthetic shirt plus cotton bandana for cooling and a great hat or better yet, an umbrella.

[Gerry Volpe]

Personally with my physiology and local climate I find cotton to be terrible even in the hottest weather. I give off copious amounts of insensible perspiration and New England often has very high humidity. Therefore cotton shirts seem to never dry very well and even mildew. I have had some luck with cotton bandanas, kept wet they help with cooling and seem to dry ok. My brother lives in NM and I have run in cotton there during the summer and barely dampened it so I tend to think it might work for me backpacking in similar hot and arid climates but have never tried it.

[John S.]

No, quick drying clothing is best all year around IMO.

[HkNewman]

In the desert summer sun, the evaporative cooling effect goes from being a negative to becoming a positive, so yes. Think Eugene had the right term for synthetics under hot, sunny conditions – stifling. I always have a Cap 1 shirt packed away though, since even a walking under a cloudless sky in a large Los Angeles park can turn into a run under a sudden cold rainy deluge.

[Aaron Reichow]

I pretty much always wear synthetics or wool. I've even been slowly replacing my white cotton undershirts with merino and synthetic- woot for white Capilene 2 Ts on SAC. One reason I like merino and synthetics that is unrelated to comfort is the higher UPF rating- untreated cotton tshirts are very low (UPF ~5), Merino is typically around UPF 25, and synthetics can range between UPF 15 and 50.

[Justin Baker]

Sorry for the resurrection. But I am confused, why would you want quick drying clothing in hot weather? That makes no sense to me. I would think holding on to moisture for as long as possible would be a good thing.

[Bob Gross]

Suppose that you were hiking the JMT, so you are climbing up steep trails to get over some pass, and then you are heading down to the valleys, and then back up again.

While you are going uphill, you tend to generate a lot of sweat. If you have a cotton t-shirt, then the sweat will hang in the fabric. Now you are generating heat that is going into damp fabric, which feels warmer. Once you get up over the pass and start down the other side, you will not be generating much sweat. The cotton shirt with sweat included will get cold since the sweat is now evaporating. So, you get chilled on the way down.

Instead, if you are wearing a synthetic t-shirt, the sweat does not accumulate as much in the fabric on the way uphill. A lot of it passes out of the fabric and you don't even feel it. So, you tend to stay slightly cooler when you are going uphill, and that is normally a good thing. Then you go through the pass and start down the other side. There isn't much sweat in the synthetic fabric to evaporate, so it does not chill you so much on the way downhill. That is normally a good thing also.

The more energetic your sport is, the more this works. You might be able to find someplace where cotton works better.

I won't even think about taking a cotton t-shirt on a backpacking trip.

–B.G.–

[Huzefa @ Blue Bolt Gear]

I think it's more important to have loose fitting, quick drying clothing. Wet cotton will stick/ cling to the skin acting as a wet suit plus reduce air movement underneath your clothing.

[Nick Gatel]

"Sorry for the resurrection. But I am confused, why would you want quick drying clothing in hot weather? That makes no sense to me. I would think holding on to moisture for as long as possible would be a good thing."

The faster water evaporates, the cooler you feel. Evaporative coolers were fairly common 30 years ago in deserts. Water trickled over a mesh screen and as the water evaporated, it removed heat from the room — this is a very simplistic explanation. This would drop the temperature in the room often by 30 degrees or more. But the humidity had to be low. In high humidity, they don't work at all, because the moisture in the air does not allow the water to evaporate much. This fast evaporation removes heat from the room. Same with your body, faster it evaporates the cooler you are.

Here are the average high temperatures where I live (F)
Jan = 71
Feb = 74
Mar = 80
Apr = 88
May = 96
Jun = 104
Jul = 108
Aug = 107
Sep = 102
Oct = 91
Nov = 79
Dec = 69

115F is not unusual in the summer. I have seen 125F. I have seen it in the 90's in Dec, Jan, and Feb; and over 100 in all the other months.

Around town or on day hikes I am not picky about what I wear. Usually it a cotton T shirt or a synthetic T shirt. I am going to be around others, cotton is best… less stink. I almost always wear shorts.

But on a backpacking trip, I need to look at what shirt is going to be best when worn 24 hours a day, for several days. Synthetic works best. It is not uncommon for me to wear no shirt or a tank top on backpacking trips, once I have my summer tan. But keep in mind that I am acclimated to the weather.

Except in shoulder seasons or winter, when I am up high in the mountains, I really don't give my clothes much thought, other than if I want an extra pocket for a camera and snacks. If I don't have a good tan, then I will wear long sleeves and long pants in hot weather to avoid sunburn… which is usually RR EcoMesh stuff. Other than that, whatever is at the top of the stack in my drawer is what I wear. I just pulled my clothes for a desert trip next weekend. Shirt is a 25 year old mesh REI tank top made of some synthetic, and similarly aged pair of Columbia nylon shorts. There was no thought put into this, other than my clothes hamper is rather full and I should have done laundry a couple weeks ago. Each was at the top of the stack.

Since I hike almost everyday, even if just for an hour at lunch, I go through a lot of hiking clothes at home… the wife does not appreciate me wearing the same clothes for weeks on end :)

I think everyone is really over-thinking this. Just grab a shirt and pair of shorts and go!

[Jake D]

Also, wet cotton tends to be pretty abrasive. when I first started backpacking i used cotton since i didn't own anything else. the shirt would get sweaty under my shoulder straps and hip belts and i'd get abrasions after a while. a few days of that and it's pretty uncomfortable.

[Ultra Magnus]

"While you are going uphill, you tend to generate a lot of sweat. If you have a cotton t-shirt, then the sweat will hang in the fabric. Now you are generating heat that is going into damp fabric, which feels warmer. Once you get up over the pass and start down the other side, you will not be generating much sweat. The cotton shirt with sweat included will get cold since the sweat is now evaporating. So, you get chilled on the way down."

As a long time desert rat, I can completely verify what you are saying… It's especially true when cycling, as your downhill speeds tend to be a hot higher than when hiking.

Now, that being said, I spent many hot summer in cotton long sleeve shirt. I used to weld for a living, and when synthetics catch a spark, they turn to napalm, where cotton only smolders and is easily put out. But the kind of cotton makes a difference… I would stay away from knit fabrics like your normal cotton T's. They get wet and sticky, cling to your body and create a high humidity micro climate, and feels like it's slowly suffocating you. Woven fabrics like dress shirts are much, much, better.

Also I would have to say for personal experience, that while a cotton T is passable, I would strongly recommend AGAINST cotton pants and underwear unless you want some serious discomfort. Once the heavy stitching is the crotch, groin, waistband areas get wet, they stay wet, and abrade you skin to no end.

BM

[Elliott Wolin]

A long time ago I too found cotton abrasive when wet, but wore it because I had nothing else. Then polypropylene shirts came out and we all wore them almost all the time (remember Lifa? I still have some).

The exception is during hot, dry weather when we dunk our cotton shirts, wear them until almost dry, then dunk them again. The cooling power overrides the abrasiveness.

[Justin Baker]

Well, to be fair I am only talking about hot, dry weather. Like 90+ degrees. Desert and California Mediterranean weather. In that situation being chilled on the downhill would be a good thing and you would feel nice, very far from being actually cold.
I am definitley not talking about the sierras or any mountain climate!!!! I am talking more like the grand canyon.

[Anthony Weston]

I'm a backpacking heretic.
I'm unable to wear synthetic quick drying shirts or merino wool etc when backpacking. I overheat.
I wear cotton. I stop, I dunk it in the stream. When I get to camp I put on my railrider shirt and hang the damp cotton up. It means I carry extra weight but I overheat otherwise. Everyone else on the trail starts out wearing fleece in the cold morning and I happily put on my still damp cotton shirt because 5 minutes up the trail I'm dripping sweat. Last summer I hiked up to Lake Vernon in 100 degree weather, several of my friends in synthetic breathable shirts were all way behind. Was I a faster hiker?, no. But I was cool in my stream soaked wet cotton. You have to do what works best for you.

[Justin Baker]

I am kinda the same way anthony, it will be 45 degrees and I will be kinda chilly and camp, but then I will hike all day in my t-shirt. My fingers and elbows will freeze though.

[Nigel Healy]

Franco, that's an interesting and puzzling argument. Is the puzzlement due to my misunderstanding?

I agree that a fabric which is wet from sweat and evaporating needs to be in close contact with skin so its cooled fabric transfers cold to the skin, that produces a slightly better performance than bare skin in that otherwise run-off sweat stays nearer to the body. That, in less words is what is a wicking baselayer.

However, I don't accept that one needs warmer thicker clothing in heat to promote cooling.

I have Merino for winter, I've tried it in summer, its simply too hot, makes one sweat more and that's with the thinnest possible Merino (which by the way is destroyed easily, quicker than synthetics.

Did I misunderstand?

I'm often in 90F dry temps May-Oct.

Cotton the hard part is getting decent seams, hot wet skin being rubbed just can't last that for more than a few hours.

[Justin Baker]

Maybe he was talking about the slightly thicker cotton shirts.

[Joe K]

My two cents…

That depends on if the weather is hot and dry, or hot and humid. Evaporation dynamics depend on the energy between the surface and the water, the temperature differential between the surface and environment, and the water vapor density differential (humidity). Since we are discussing “hot” weather, we can assume the temperature differential is constant in the comparison below.

The energy between the surface and water:

Consider two surfaces: One which is hydrophobic (water beads up), and one which is hydrophilic (water spreads out / absorbed). With the hydrophobic surface, water is being pushed away by the surface – the attractive forces are small and this recognized as a low surface energy interaction. With the hydrophilic surface, water is being pulled to the surface – attractive forces are larger and this is a high surface energy interaction.

For water or sweat to evaporate from a surface, energy needs to be transferred to the water to transition it to vapor. This energy mainly comes from two sources: the surface (skin), and the surrounding air. You probably already know that the cooling effect felt when sweat evaporates is due to heat energy transferring from the skin to the sweat.

• Synthetic fabrics have a hydrophobic character and there is less (relative to cotton) attractive energy between water and the surface. This means less energy is needed to cause evaporation, which means there is less cooling effect per an equal volume of water compared to cotton.
• Cotton has a very hydrophilic character and there is more attractive energy (relative to synthetics) between water and the surface. This means more energy is required to cause evaporation, which means that when energy is transferred to the surface there is more cooling effect per an equal volume of water evaporated compared to synthetics.

Effect of the vapor density differential (humidity):

During the summer in southern Arizona, the temperatures are hot (often above 100F) and the air is very dry. Not too far south, in the Gulf of California, the temperatures are cooler and the air is more humid. This creates a difference in temperature and humidity which causes weather changes. The moist air wants to spread out and it flows toward areas where there is less water in the air – Arizona. By the afternoon around 3 or 4 pm, when the temperature in Arizona has cooled, the moist air which has traveled from the Gulf begins to condense in the atmosphere causing – you guessed it – desert monsoons.

This same phenomenon of humidity differential has an effect on sweat evaporation. We already know this. The more humid the surrounding air, the less sweat wants to evaporate. If there is less attractive energy between sweat and a surface, then it will be easier to evaporate. If there is more attractive energy between sweat and a surface, as with cotton, evaporation will be harder. So, in a humid environment we’d want a hydrophobic (synthetic fabric) surface to help push sweat to evaporate. The higher the humidity, the more synthetics help. In a dry environment, however, we don’t need the extra push to help sweat evaporate – the “push” is given by the difference in humidity of the very wet “surface” and the very dry air. The drier the air is, the stronger this “push” is. Cotton’s cooling effect comes into play when the air is very dry.

• A note on the effect of wind: When sweat evaporates off your skin or clothes, a microclimate is created near the surface and this microclimate is humid. Wind helps evaporation by dispersing this humid microclimate and replacing it with relatively less humid air. This is especially important with cotton for the same reason mentioned above. With cotton, we need the help of drier air to cause evaporation.

So, in hot humid weather synthetics are the way to go. If you wear cotton, your sweat won’t evaporate and you’ll be hot. In hot, dry weather, you can wear synthetics or cotton. However, I recommend choosing the material with the greater cooling effect: cotton.

BUT… what about breathability and chaffing? Breathability is important to allow water vapor to pass through your clothes to the outer environment. Synthetics are often thought to be more breathable. Breathability has to do with how porous a material is and the size of the pores. Synthetics can be spun into thin filaments and very breathable fabrics can be made from them. Cotton can also be very breathable, if it is loosely woven. The member who recommended threadbare woven cotton shirts over knit t-shirts was absolutely correct.

Everyone knows cotton chafes. If you want to take advantage of cotton’s cooling effect in hot, dry environments, only wear it in areas where there will be no rubbing and adequate ventilation (not socks, crotch, and armpits!).

In summary:

In hot, humid environments:

• Synthetics aid evaporation
• A breathable synthetic fabric must be chosen (obviously not a nylon rain jacket)

In hot, dry environments (especially with wind, like in most deserts)

• Synthetics aid evaporation, but have less cooling effect because of lower surface energy
• Cotton slows down evaporation, but the dry air and wind help speed up evaporation.
• Cotton has a greater cooling effect per equal volume of water evaporated
• Since cotton slows down evaporation, the cooling effect is prolonged (cotton knows how to ration water)
• Whether wearing cotton or synthetics, choose a fabric with a breathable weave pattern.
• Cotton/synthetic blends are another option (breathability still important).

Other notes:

• In order to benefit from the evaporative cooling effect from clothes, the clothes should be contacting the skin: true. Otherwise the cooling effect is not as noticeable. It is still important to keep the sun off your skin and block radiation, so loose clothing isn’t bad.
• The color of the clothing makes a small difference in heat transfer if the density of the fabric is low as with synthetics. Cotton is more dense than synthetics, so lighter colors should be chosen. However, lighter colors probably reflect UV rays better.

[Anonymous]

On another thread, dealing with a similar issue/question, for hot and very dry desert type conditions, I recommended a breathable, thinnish, cotton spandex blend-somewhat form fitting, very dark colored shirt, and over that, an even more breathable, very light colored, sort of “half poncho’ made out of a more stiff, but absorbent fabric like linen or ramie.  I say half poncho because no hood, not quite as wide, and shorter than a typical rain poncho–particularly in the front.

Good protection from the sun, while maximizing and prolonging evaporative cooling next to skin for those super low humidity and hot conditions.

Another poster pointed out that if there is a very hot and strong wind blowing, you’d probably want to use a more air blocking fabric outer to help create and stabilize an inner micro climate.  Makes sense, though I haven’t experienced that myself, though I’ve spent some time in deserts.  Likened it to the difference between a regular toaster oven and a convection one. The super air convection of hot wind can rob the cool, moist air next to skin and essentially “cook you faster” so to speak. Kind of an inversion of the same principles of what happens in relation to insulation, and trying to stay warm in very cold conditions.  In that case, might be good to bring along an over sized windshirt/jacket?

[Author]

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