Updated: Sep 27, 2019
By Hala Petrasdottir Buckle up campers, we're talking about MOISTURE.
Here’s the short version: Different fibers have different properties and react to environmental/atmospheric junk in different ways. If you keep these properties in mind as you build your kit, you’ll be able to choose garments and equipment that are better suited to your needs, and you’ll be happier, healthier, and look fly as hell.
Here’s what the heck I’m talking about when I say “moisture-wicking”, from the mouths of REI themselves so you know it’s legit: https://www.rei.com/blog/hike/what-does-moisture-wicking-mean
Moisture-wicking is not the same as absorbent! Absorbent is when the fibers, y’know, absorb water, but wicking is when they move the water through and release it again—think of a candle wick, bringing wax/oil to the end of the fibers so it can burn.
I’m limiting this rant to cotton, linen, and wool, because those are the ones that I can yell about the loudest. If you want to look into the various moisture-wicking and insulation properties of synthetic fibers, godspeed and please write your own rant when you have time so others can learn from your mistakes—er, research!
Cotton DOES NOT wick moisture. That means when cotton gets wet, it stays wet. It also means that when wet, cotton does not insulate well. This is because it’s, y’know, full of water, and wet cotton holds/carries/loses heat in a completely different way from dry cotton. Science!
Cotton IS GOOD FOR middle layers, between your innermost layer and your outermost layer. This is so it can be mainly protected from inside moisture (sweat) and outside moisture (rain, snow, fog) and can insulate the way it's meant to. Dry cotton is useful cotton!
Cotton IS BAD FOR any layer that is directly against your skin. It’ll get wet, either from rain/snow/outside stuff or because you’re running around getting sweaty, and then it’ll stay wet, end up clammy, and ruin your entire weekend. Best case, you feel and smell kinda swamp-assy; worst case, you’re at risk for heat- or cold-related problems like heat stroke or hypothermia.
Fun fact corner: The heatstroke would be because warm, wet cotton can prevent your body from losing heat in its normal efficient ways; continuing to sweat into wet cotton doesn’t actually cool you down at all. The hypothermia would be if you’re sweaty from being insulated or running around, the cotton gets wet, and then you stop running around and the temperature of your clothing and skin drops. Wet cotton takes way more effort for your body to keep warm (which it has to if it wants to stay warm inside the wet cotton), and basically acts like a wearable refrigerator, which at a cold or outdoor event is unpleasant and literally leads to hospital trips so please just do not.
Another fun fact corner: The reason you see so many LARPers and reenactors using canvas tents is that when cotton canvas gets wet, the fibers swell (to hold onto the water) and end up taking up more space. This means there are fewer/smaller teeny holes between them, and fewer leaks in the fabric because surface tension—unless you lean something up against the wet canvas from the inside or outside of the tent. That gives the water a place for surface tension to break, and you end up with a drippy puddle. This also happens at seams, and at any upright support poles. If you can keep all your stuff inside the tent at least a couple inches away from the tent walls and poles at all times, and ideally also off the floor, you’ve got yourself a cozy dry setup!
Linen DOES wick moisture. That means linen gets wet but it doesn’t hold onto the moisture the way cotton does; the fibers themselves aren’t actively trying to keep the moisture in. When you sweat directly into a linen tunic, the water finds whatever available spaces to evaporate out of, so although you’ll still be wet in the short term, as soon as you aren’t currently sweating or getting rained on any more the fabric will start losing the moisture and allowing for normal air and heat transfer/breathing to resume.
Linen IS GOOD FOR layers closest to your skin, so that your body moisture has the best chance of doing its job: leaving your body, and then leaving the immediate area, to help you self-regulate body temp. Linen is also good for lining outer garments like wool cloaks and hoods, because when the wool gets wet, it’s good to have the linen as a barrier to help everything dry out again, instead of the wet just transferring directly from the wool to any cotton or whatever else you’re wearing.
Linen IS BAD FOR outer layers and insulation by itself, if you are cold and trying to stay warm. (This is mostly anecdotal; I’ve never had great luck staying warm with only linen garments; in concert with cotton and wool is the best combo I’ve found.) If you are trying to stay cool, linen’s freakin’ great and you should layer the heck out of it. Think about the local clothing in hot places like the Middle East or North Africa; you see more layers and full coverage than low-coverage clothing, because it’s actually cooler (temp-wise and fashion-wise!) to wear loose, flowing clothing that allows for sweat to evaporate, than it is to be sunburned with no cover.
Wool DOES wick moisture—but differently than linen! Wool will get saturated and wet, but it allows for the water to evaporate more than cotton does, so you can feel that the fabric is wet or heavy, but it won’t transfer as much through to whatever’s on the inside (lining fabric, your skin, small dogs, etc.) Wool also doesn't lose its insulating properties when it gets wet, like cotton does.
Wool IS GOOD FOR moisture barriers between you and nature (cloaks, blankets, outer layers, covering your bed/cot so that it doesn’t get all dewy and squicky)
Wool IS BAD FOR layers directly next to your skin; besides often being itchy, wool just insulates super well and if you don’t give yourself a bit of barrier it’ll probably make you overheat. Remember: your body is pretty good at regulating its own temperature within a moderate range, so letting it do its job as much as possible is a good use of evolution.
Fun fact corner: You can totally wear wool in hot weather! You just need to find the lighter-weight, more breathable weaves. Look for “summe-rweight” wool rather than “mid-weight” or “heavyweight”. And wear linen underneath!
Okay fine socks are not a fiber but they are VERY IMPORTANT.
Cotton socks will get sweaty-gross and wet in any weather, and they will stay wet, and if you don’t take them off and let them/your feet dry, you’re gonna end up PRUNY and SMELLY and it’s NOT GOOD that is how you get TRENCHFOOT!
But mostly, cotton socks get wet and then stay wet, so your feet will get super cold as soon as your body heat isn’t enough to sustain the warm temperatures. DO NOT SLEEP IN COTTON SOCKS!
Wool socks will also get sweaty and damp, but because of the insulation properties of wool your feet will at least stay a lot warmer. Please still remember to take the socks off and let them and your feet dry or you will get TRENCHFOOT and be SAD. Do not sleep in wool socks either (unless they’re fresh and dry and you don’t expect to sweat a ton during the night).
The best way to stay warm while sleeping is barefoot (either naked or in dry, un-constricting clothing) under good blankets or in a sleeping bag. Direct skin contact (either with your own skin or another consenting adult's!) is the best way to encourage and maintain good core body temperatures. This is also why mittens are warmer than gloves, and sleeping bags are an excellent excuse not to wear pants.
Important note about fiber content
Any of these natural fibers needs to be present in a high enough concentration in the fabric’s makeup to actually present these properties. If you have a 30% linen/70% polyester blend, it probably won’t actually wick and breathe the way you want. If you have a 25% wool blend, it likewise may not insulate the way you want, or may not hold/distribute water the way you expect.
If you’re buying from a physical store, and they don’t know the content, ask if they’ll help you do a burn test. This is a completely legitimate thing and you should not feel weird about asking. A burn test is when you cut a small corner (like, a couple square inches) from the fabric and literally light it on fire.
Why would you do this? Because, as at the top, different fibers have different properties. Polyester and other plastic-y synthetics will melt, rather than burning (and smell bad!). Burning wool smells like, well, burning hair. Burning cotton smells clean; burning rayon smells like burning paper; burning linen also smells vaguely clean and plant-y. If you want help with any of this check the internet!
My general rule is that I want at least 40% [fiber I’m aiming at] or I won’t buy the thing. Sometimes I’ll be real picky and want at least 50%. The nice thing about this is it means that you CAN use fiber blends (which are often cheaper!) and still get the effects you want—just be careful you don’t go too low on the main fiber percentage.
TL;DR: Linen right up against your skin as much as possible; cotton for in-between layers of insulation; wool for outermost layers. Dry socks are the best socks. Constricting clothing, including socks and gloves, will not keep you as warm as giving your skin warm air to be next to other skin in (like the inside of a mitten, or under a cloak, or in a sleeping bag).
Learn the signs of hypothermia. Learn the signs of heat exhaustion and heat stroke. Stay hydrated, but also stay sweating, and that includes letting your sweat evaporate. Be safe, have fun, and if you're going to kill each other, kill each other, but y'ain't gonna do it on my beat!
Hala Petrasdottir (Fish)