Baselayer science is more hardcore than a Pussycat Dolls video. It’s more difficult than reading quantum mechanics, in Chinese, while solving a Rubik’s cube using your nose. But, like a rhinoceros in ballet pumps, I’m going to dive right in, before these similes get any worse.
Why are baselayers important?
I’d argue that a baselayer is the most important clothing layer that you wear. Why? Because it’s next to your skin. You wear it all day long, unless you plan to go streaking, and comfort is measured at the skin level, not on the inside of your waterproof jacket.
A good baselayer can be used year-round and in every activity from cycling to mountaineering – there’s not many garments you can do that with.
What is the job of a baselayer?
The classic answer to this is ‘to wick sweat away’. You could counter this statement by saying that merino baselayers – which have an excellent reputation – wick pretty badly. You could also argue that Helly Hansen’s classic polypropylene Lifa fabrics do not wick at all, yet a lot of runners still think they’re the best baselayers on the market. In short, I think wicking is a bit of a misnomer with baselayers. Here are the four criteria I think are important for baselayers:
- They must keep you dry
- They must keep you at a comfortable temperature
- They should smell, look, and feel nice. They also need to fit (which is part of 1, 2, and 3).
- They must be durable and easy to care for
Note that nowhere in that list is ‘keep you warm’ – a baselayer should not try to hold in masses of heat, as you can’t take it off easily in most situations (particularly if you’re female).
If you are too cold, you can put layers on top, but providing lots of insulation is the job of your midlayer(s), not your baselayer.
Keeping you dry
This is where people will be shouting “wicking!! Wicking!!” …and they’d be… sort-of right. If a baselayer must keep you dry then it should allow direct evaporation of moisture from the skin to the atmosphere or into your clothes and/or it should be able to wick sweat from the skin. The level of absorbency of the fibre is also important – of the common fibres used in clothing, cotton absorbs the most water, wool next, then polyester, then polypropylene. If you are not exercising, and are instead sat at a desk in a comfortable environment, any of the above fibres will keep you dry enough, but if you start sweating more (maybe your boss arrives at your desk and tells you that you are fired; alternatively you leave your desk and run up and down the stairs for fifteen minutes) then the cotton will become saturated – the wet-t shirt look – as it absorbs huge amounts of liquid; the wool will also absorb a lot of sweat, thus taking a long time to dry. The polypropylene, meanwhile, even when saturated, will have only absorbed a fraction of the sweat, meaning it dries faster. Why is keeping dry important? Because it feels horrible to have wet skin, and wet clothing makes you cold (see here).
Direct evaporation is all about the air getting to your skin, and is a combination of lots of different factors including the type of knit used in the fabric, the thickness of the fabric, the way it fits… it is really complicated. However, the way I think of it is simple – a lightweight and open fabric will allow more direct evaporation of liquid from your skin. So, a Brynje-type mesh top will allow huge amounts of air onto your skin to transport moisture away super-fast, a lightweight Helly-Hansen top will do the same, but an ‘expedition weight’ baselayer weighing 300 g will not.
Wicking is a whole other subject in itself, but wicking (capillary wicking if you are feeling clever, and do feel clever, you deserve it) is the spontaneous transport of liquid that occurs when liquid would rather come into contact with a solid surface, than more liquid like it. Imagine the liquid to be like a group of desperate male blokes, who would rather spread out to meet women than keep each other’s company. What people forget with wicking is that there are two types – transverse wicking and planar wicking. Both are important, but one is useless without the other.
Transverse wicking is the movement of liquid from one side of a fabric to the other, such as from your skin-side to the face-fabric side. This one is crucial, and is what keeps your skin dry in the absence of air flow. Planar wicking is what allows transverse wicking to work faster, moving sweat from high concentrations to low concentrations through the plane of the fabric (eg. from the armpit to the side of your torso), enabling more surface area to get rid of the sweat.
Small diameter fibres in a fabric lead to greater number of channels for sweat to flow through, and small channels between these fibres are more attractive than big ones, making wicking happen faster. Wicking is also sped up by increasing the cross-sectional area of fibres (fibres such as Coolmax are shaped almost like a key, with loads of notches along them). As a result, not all polyesters are equal, and that £50 baselayer might well be a whole lot better at moving sweat than the £3 one from Tesco (remember that the diameter of the fibre, the shape of the fibre, the coatings on it, the way it is knitted, and the weight of the fabric all impact on performance). In general, polyester and wool wick well; polypropylene less so.
So, to keep dry, let’s just say that a baselayer should allow for direct evaporation (it should be as open as possible), should wick (needs the right type of fibre), and shouldn’t absorb too much water (should be thin, lightweight, and not cotton!)
Keeping you at a comfortable temperature
This one is seriously hardcore, but bear with it (I told you it was a Pussycat Dolls video, didn’t I? This is possibly more like Rihanna and Beyonce starring in an advert for Cravendale). Obviously, to be at a nice temperature you shouldn’t get too hot, or too cold, and we’ll deal with them in turn:
If you risk getting too hot, wicking is bad. Yes, bad.
That’s because sweat that doesn’t evaporate is useless – it hasn’t evaporated so hasn’t cooled you down. Direct evaporation, however, is good, as all that sweat has evaporated and that cools you off.
If you risk getting too cold, wicking is good, as your sweat does not evaporate and instead moves away slowly. That direct evaporation, however, suddenly becomes a nightmare and you get too cold too fast as your sweat ’vaps away.
So, we’ve now got a position where the two things are in opposition! What do I do on a day when I might get too hot and too cold, such as any day out in the UK hills?!
The answer is that you can’t win, and therefore I’m going to argue that the most important criteria for a baselayer to keep you at a comfortable temperature is to use a thin one, thus minimising the amount of moisture it will absorb, reducing the chance of you overheating, reducing the distance that moisture has to wick, and also making your midlayers more useful.
Smell, look, and feel
Some synthetic tops get a really bad reputation amongst their owners, and perhaps amongst their owners’ families, for stinking. This is often justified. Merino wool, however, stinks far less often, and that’s because wool is amazing, nature’s second most incredible composite (after feathers). In short, no matter how fancy a coating is applied to a synthetic fabric, merino is the way to go if you want to wear your top for long periods. If I go backpacking my synthetic baselayers will be seriously offensive after 3 days; after 7 days I’d come back and probably not even bother washing my merino ones.
Look and aesthetics of a baselayer is down to your taste, and beyond the scope of this blog, but one point worth making is super-tight baselayers look better on people they fit – if they are super-tight because you are super fat it may cause offence. Also, no one looks good in mesh.
The feel of a fabric is important, and some people argue that merino fabrics feel itchy. I think that’s probably because you’ve bought a rubbish one. Prickle and tickle from fabrics result from stiff fibres sticking into you or from roughness on the fibre surfaces. British wool is coarser than merino, but merino is often as thin as synthetic fibres used in baselayers, so really shouldn’t be a problem. However, if you know that even fine merino feels itchy for you, then don’t buy it.
Durability and ease of care
This is where there’s another real difference between wool and synthetic fibres: wool is not as durable, and is harder to care for than polyester or polypropylene. I have synthetic baselayers that I have worn over 300 times and that look ‘as new’, yet woollen baselayers of the same vintage have holes at the cuffs and bobbled shoulders. Synthetics are also easier to wash – just stick them in the washing machine and they aren’t fussy, they dry quickly, and usually don’t mind being tumble dried. Merino tops tend to be picky on these points, but this is countered by their awesome resistance to stench, meaning they don’t need to be washed as often. If you are washing your merino baselayers after every wear I’d urge you not to – your bills, your clothing, and the environment will much prefer it if you only wash them when they actually need it (eg. stained, filthy, sweat patches, etc.).
What baselayer should I buy?
Now at risk of repeating myself, I’m going to say your most important priority should be to buy a thin and lightweight baselayer, regardless of what activity you are doing. If you are going somewhere cold then use a thicker midlayer, or two baselayers. Beyond that…
If you are going to be working hard and sweating a lot – synthetic, as it absorbs less water than wool. Polypropylene or mesh polyester are possibly the best.
If you are going on a long trip without easy washing facilities – merino all the way, or your friends will disown you.
If you are going to be wearing the baselayer as your only layer all day – think of your friends; don’t go for that outrageously tight mesh baselayer. Also, if you’re in the sun, you can get awful sun burn (as demonstrated once by well known peddler, Chris Froome.)
If you are going to be wearing stuff over your baselayer all day – mesh! It’s the best on allowing direct evaporation of water from the skin and polyester meshes also wick very well.
If you have limited budget – buy the best one you can in a sale, and get a synthetic one as it should last for ages and will be cheaper at point of sale. Make sure it fits you and buy a colour that you actually like, or you’ll buy two and so spend more.
If I could only have one baselayer – I’d have a synthetic one with long sleeves and a zip to mid-torso, in a lightweight fabric.
My dream baselayer – synthetic again, with long sleeves and long zip, with a under-helmet hood, and weighing 150 g in a size medium. They’re rarer than hen’s teeth, though – mine was ordered from Canada by a friend of a friend. And, it is absolutely amazing.
I hope this has proven useful. Baselayers are really complicated, but it’s worth realising that wicking is not the whole story, and that each fibre has its place. I think if there’s one thing worth remembering, it’s that baselayers are there to keep you at a decent temperature, and to keep you dry – they’re not to keep you warm, as that’s the job of a midlayer. When it comes to buying time, think about what you’ll use it for, what sort of trips you go on, and whether you can pull off the mesh baselayer look…