Cotton kills! Why the wrong clothing can be lethal

If you just go for the occasional walk or ride, you may wonder why the outdoor gear shops are full of clothes made from artificial fibres – what’s wrong with jeans and a t-shirt anyway? This is a quick look at the materials technology science behind the ‘Cotton Kills!’ campaign.

Like you probably do, I wear cotton a lot of the time. Most t-shirts, shirts, jeans, trousers and lightweight jackets are made largely from cotton as it’s relatively inexpensive, easy to wash and comfortable to wear.

If you’ve been out on a few walks wearing jeans and a t-shirt you probably wonder a bit about the ‘proper’ walking gear you see on sale made from wool, polyester and similar fibres. Is it just a fashion thing? Or is it a clever scam to make you spend more on expensive outdoor clothing?

While cotton is a good material for walks on dry days, it begins to create serious problems when it gets wet from rain, sweat or fording a stream.

Fine in dry weather, jeans and cotton jackets lose almost all insulation properties when wet and take ages to dry

Fine in dry weather, jeans and cotton jackets lose almost all insulation properties when wet and take ages to dry

When cotton gets wet, it stays wet. At the same time, its insulation abilities drop to almost nothing (just a cotton layer is almost the same as being naked!) On a hot summer’s day, this can actually be a good thing – damp cotton will keep you cool.

(As an aside, cotton underwear gets damp from perspiration quickly, and can chafe badly when it is wet. In hot conditions artificial fibres or very fine wool like merino can be a lot more comfortable – or just go commando)

Unfortunately, in this country, hot summer days are the exception rather than the norm. It’s especially dangerous for hill walking. Combine an unexpected shower with lower air temperatures and higher wind speeds, you can suddenly find yourself under-dressed. You can easily lose heat more rapidly than your body can generate it, leading to hypothermia and potentially death.

If you are avoiding hills and are near shelter or there’s zero chance of rain, cotton can be fine – but the rest of the time you will need to look for another option.

​Here’s some alternatives to cotton

Polyester

One of the most common man-made fibres, it’s light, insulating, and highly breathable. It’s also ‘wicking‘ (pulls moisture away from the body so you don’t feel sweaty) and actively repels water, so dries very fast.

The breathability comes with a down side – there’s almost no wind proofing unless a layer of another material is added.

It’s most often seen as a mid-layer in a fleece, but can also make a great base layer next to the skin. Base layers tend to get smelly if you wear them for more than a day.

Polypropylene

Like polyester, this man-made material is lightweight and soft, has high ‘wicking’ ability and quite good insulation. Makes a great base layer in colder temperatures, but like polyester does need washed regularly.

Merino wool

A very fine wool, soft enough to be worn next to the skin. It’s breathable enough to keep you cool on warm days, but still provides insulation when it's colder. Does not dry as fast as the man-made fibres, but still provides decent insulation when wet. It tends to be more expensive and not as durable as man-made materials, but you can wear it for a few days in a row without the smell becoming offensive.

Wool and tweed

Ordinary wool tends to be itchy if next to the skin, so it’s best used as a mid layer in a jumper, although I find wool based trousers or socks fine. Other than that it’s actually a great material, and has been used for traditional outdoor clothing for centuries.

Wool makes an excellent insulator even when wet, has good ‘wicking’ abilities and is very durable and even reasonably fireproof. With the natural lanolin oils and a tight weave, it can even be moderately waterproof.

Use wool as a mid-layer in wet conditions, or a top layer in dry conditions. However, wool is relatively heavy and takes a long time to dry once it does get wet.

Down

Made from the fluffy insulating layer underneath feathers, most commonly taken from duck or geese. It’s a great insulator, lightweight and easily compressed (squashed) to fit in a bag. You will see down used in expensive ‘puffy’ jackets and in top-end sleeping bags. However, like cotton, down is useless once wet and takes a long time to dry. Some more expensive jackets combine down with a waterproof shell to protect the insulation. Down is best used in cold, dry weather and tends to be a pretty expensive option.

Nylon

Another synthetic material, nylon is tough and usually waterproof, so it is often used for an outer shell.

PU-coated nylon is waterproof and not breathable at all, so it’s OK for an emergency waterproof but very sweaty if you wear it all day. Non-coated nylon is breathable but not waterproof, so you mainly see it used in ‘windproof’ tops.

Like most man-made materials, it does not cope well with fire and will melt or burn if it gets too close to a stove or gas lamp.

Breathable membranes

Often known better by their brand names such as Gore-Tex, these man-made materials offer both waterproofing and breathability. The membranes themselves are quite fragile, so are generally sandwiched between other materials.

Most 'proper' outdoor gear will use a breathable membrane. They are rated according to how waterproof and how breathable they are - generally more expensive ones tend to perform better.

All breathable membrane clothes need regular washing to maintain performance.

Waxed cotton

You know we said that cotton is generally pretty poor for outdoor clothing? Well, it’s not entirely true. Waxed cotton is making a bit of a comeback, especially with the latest offerings from Fjallraven, Barbour and other brands. It’s a heavy cotton that has a wax melted into the fabric, making it waterproof and a bit breathable, although not very warm on its own. The wax can be re-applied as needed, giving them great durability.


Of course, a lot of outdoor gear will blend different fabrics, or use them in layers to improve performance. You will even sometimes see cotton blends, but in general any outdoor clothing designed for the British weather will avoid cotton.

I've not covered some of the more unusual fabrics such as bamboo-based materials, neoprene, aramid and leather. There's also a host of brand-name fabrics that combine basic materials or modify them in some way.

What’s your favourite materials and why? Tell us in the comments.

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