Fashion always seems to go in full circles, and this is no more truer than with thermal underwear. For centuries wool had been the winter underwear of choice but this changed with the invention of man made yarns in the 1940s and 50s. New materials made from these raw materials lead to the spread of the synthetic base layer towards the end of the 20th century. However, over the past decade the market has seen a resurgence of performance woollen underwear, with synthetic base layers being much maligned, albeit by woollen vested interests.
Before people start to dispose of their ‘plastic’ underwear and adopt a more ‘environmentally friendly’ woollen clothing system, they should really consider the following points:
Wool can be itchy. There is no getting away from it. If people have sensitive skin then it doesn’t matter how soft the wool actually is, it is going to irritate the wearer. Sometimes this can be psychosomatic, but that is no comfort if you are on top of a mountain scratching away.
Synthetic fabrics on the other hand have a very soft handle, especially polyamide, that rarely irritates the skin. The long smooth fibre profile glides over the skin rather than scour it. This smoothness also helps other items of clothing to glide over a synthetic base layer, helping to prevent rubbing and chafing.
Being a natural product, wool will degrade over time. This was fashionably demonstrated by HRH Prince Charles who buried an old woollen jumper. Although this composting ability is seen as a major advantage it does have the disadvantage in that the longevity of a woollen base layer is short. You will be lucky if one set lasts you a season if used regularly.
In comparison, a synthetic base layer will not degrade, well not in your lifetime anyway. Viewed mainly as a negative to the environmental lobby, this is in fact a positive – a thermal base layer for your lifetime. Most people only change their synthetic base layer if a) they loose it b) they boil wash it and shrink it c) change body shape that means the fit is no longer good d) fancy a different colour.
Better Moisture Management
Wool acts a bit like a sponge, soaking up moisture when in contact with it. Defenders of this process will state that it doesn’t feel wet, it’s just absorbed internally. OK, this is true for about 25% absorption, but if you fall in a body of water you are going to have a very heavy base layer. Just feel the weight of a washed jumper before the spin cycle.
With a synthetic base layer basically being made form plastic, water absorption within the yarn is very low, and is in fact 0% in polypropylene base layers, effectively making them waterproof. The construction of the garment will dictate how much water is actually held (rather than absorbed) but this is often marginal. With these base layers, and especially polyamides, you can impregnate hydrophilic treatments in to the yarn itself to further aid moisture movement.
Most people will have probably shrunk a woollen jumper at some point in their life. Its a natural reaction by the wool fibres to heat, water and mechanical action to want to revert back to their original curly shape. Think of straightened frizzy hair after getting rained on. Some woollen base layer can be washed on a cool cycle with no spin, but most recommend hand washing and line drying, which is ideal in the summer, but a pain in the bum in the winter when you are going to use them the most.
Don’t get me wrong, synthetic base layers will shrink at high wash temperatures, but put them on a washing machine spin cycle at 30-40oC and you will have no issues. Due to their low water absorption, they will also dry much quicker.
More Environmentally Friendly
If you interviewed most outdoor enthusiasts, the vast majority would probably believe that woollen base layers are more environmentally friendly than synthetic versions. You can understand why. It’s a natural product that rots down and absorbed back in to the earth. But scratch a little further and all is not as it would seem. Wool is not something you just sheer off the back of a sheep and wear. There are a lot of energy intensive processes involved to get a finished product that is relatively soft and user friendly. So if you are having to buy one woollen base layer a year, over your lifetime that is a lot of energy and resources used.
In contrast, a synthetic base layer may not be biodegradable but it will last a long time and is a lot more robust. You may only ever need one thermal set in your lifetime if you are lucky enough to stay the same shape. Once you have finished with, it can also be recycled in to the next base layer for someone else lifetime.
For just coming off a sheeps back, the cost of a finished wool product is very expensive, mainly due to the amount of processes involved. A new set every year is going to be cost prohibitive to a lot of people, especially with the added risk of laundry damage and natural wear and tear.
A good quality synthetic base layer of comparable weight and style will probably be around 15-25% cheaper. Once you start to multiply the cost by the lifetime of the garment, you are getting a lot more bang for your buck with a synthetic base layer.
When Wool Should Be Used
There are certain situations where we would advise woollen base layers to be used. If any person has the possibility of contact with fire such as in the aviation industry or the emergency services, then woollen base layers are ideal, as the fabric chars rather than burns. There are also industrial applications, such as welding, where sparks or high temperatures may be around the wearer.