Which materials do you choose for active base layers

The first rule of anything high activity or outdoor is cotton kills. The reason is that cotton will absorb tons of water then take eons to dry out. Even in the summer that water can mean the difference between a damp uncomfortable day and getting sick or in the worst case scenario needing a full evacuation. All that water also generally leads to more chafing which greatly decreases the comfort of your activity. The material you wear matters in your comfort and in your safety. It especially matters in your base layers as they are in direct contact with your skin.

Outside of the rule that cotton kills what you don’t want is any fabric that absorbs a bunch of water then takes a while to dry out. Fabrics like bamboo feel glorious but they take on more water than a fabric like Merino wool. Rayon Lyocell and Modal also fall in to this ‘tree product’ category as they’re made from tree pulp and some of them actually absorb more water than cotton garments, up to 50% more for Lyocell.

So that old adage ‘cotton kills’ may be more accurate if we amended it to say that ‘tree fibre fabrics and cotton kill’.

Some of these tree fibre fabrics like Lyocell are naturally hypoallergenic which means they don’t smell bad because they stop bacteria growth. I don’t think that this feature is a reason to trade in for the high water absorbing properties of the fabrics though. Merino Wool also naturally stops the stink and absorbs significantly less water than tree fibres.

If we exclude tree/plant fibres from our options in outdoor clothing we are left with 2 broad categories: Wool and Synthetics.

Synthetics as base layers

Synthetic fabrics like Polyester or Polypropylene offer some distinct advantages over tree fibre fabrics, namely they doesn’t really absorb water and can be very strong. Polyesters will dry fast and wear hard and well.

When you have a ‘wet’ synthetic shirt the fibres themselves haven’t really absorbed any water, it’s just trapped in the spaces between fibres. Some companies shape their fabrics to have a ‘ridged’ profile which aids in the drying time due to more surface area being presented. Reduced drying time means that the fabrics won’t take on a funky smell as fast.

Another big advantage to synthetics (at least for the manufacturers) is that they’re cheaper than wool, particularly polypropylene (polypro). The draw back of polypro is all the bad you’ve ever heard about synthetics. It stinks quick, wears poorly and is very delicate to launder. This is why it’s pretty much all a blend of the cheaper polypro and the more expensive, harder wearing polyester or some other fabric to give more strength.

The big drawback to synthetics is that they often start to stink and quick. Where other natural fibres like wool can pick up a funk after a lot of use many synthetics pick up a funk with in a few wears.

To combat this companies come up with treatments to kill bacteria in their clothing. Some of the most popular current technology is to treat the garments with silver. We’ve got an upcoming longer article on silver treated fabrics. Basically a bunch of the silver washes out right away and that’s silver in our water system which doesn’t sit well with me.

Regardless of the treatment the company decides to use the fact is that this is a treatment applied to the fabric. It is not an inherent property of the fabric. This means at some point it’s going to wash off/out and then you’ve got a funky smelling garment again.

Wool as a base layer

Merino wool is the current rage in the outdoor industry, but long before we had merino stamped all over everything we just had plain old wool sweaters to wear.

Wool has a few benefits going like the fact that it’s naturally hypoallergenic. It has a higher ignition threshold (where it catches fire) than many other fabrics. It’s breathable, easy to care for, decent insulator without getting ‘hot’ on warmer days.

The biggest draw back to wool versus synthetics is that it does absorb more water and take longer to dry out. Wool doesn’t absorb anywhere near as much water as cotton, but unlike synthetics it has 2 ways it can contain water.

First the inner core of wool is hydrophilic (likes water) so when water gets through the hydrophobic (doesn’t like water) outer sheath it sits comfortable inside the fibre.

The second place the wool contains water is in between the fibres which is the only place that synthetics can take in water. Wool generally has more crevices to hold water since it’s not a smooth piece of shaped plastic. It’s a fibre with a jagged edge and lots of nooks and crannies for water to sit inside.

Ultimately this is a tradeoff since the structure of the fabric gives it both it’s water absorbing capacity and it’s ability to be warm. Just like it holds water in all those little crevices and inside the core of the fibre, it holds your body heat as well.

One benefit to wet wool is that as it absorbs water it starts to give off some heat in a process know as ‘the heat of sorption’. No that doesn’t mean that wool will suddenly raise your body temperature a bunch if it’s wet, but that does mean that if you have a wet wool shirt on you’re likely doing less work to stay warm than with a similarly wet synthetic or cotton shirt. In your regular wear it probably just means that a damp wool shirt at the top of an alpine ascent will still feel comfortable with the sweat soaked up in it.

On the smell front, merino wool does a stellar job and not getting stinky. My set of shirts include a number of Tasc

Merino shirts that get worn around, worked out in, hiked in, paddled in, just generally used and while my wife says she can detect just a bit of an odour when she’s folding laundry she can’s smell anything when I’m wearing them. This is not her experience with my synthetic shirts, even those coated with silver of some fashion. They’re not terrible and she’s not making me relegate them to only the backcountry, but she says they always have just a bit of a smell going if you get right up close. Close enough that only my wife and kids should ever have the opportunity to notice the issue.

The key takeaway is that if you’re planning to get out in the backcountry stay away from your cotton shirts. Get something synthetic or wool. My emerging preference is Merino Wool shirts, specifically from Tasc. Keep your eyes on the site to see reviews of technical tops/bottoms available for adults and kids.

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One Comment

  1. […] I’m going to talk just a bit about the materials that each of the pairs of these underpants are made from. If you want much more depth on the differences between Modal and Lyocell and Rayon, I’ve got a long post dedicated entirely to base layer materials. […]

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