Smart fibres and smart fabrics

A little while ago I was asked to speak on a panel discussing smart fibres at a fabric conference/show. Unfortunately I was unable to attend but I wrote a mini essay on the subject. It’s copied below, and I’ve stuck in some photos to try and illustrate the point.

Fibres which thermoregulate are the dream ticket – we don’t want fibres to keep us warm or cool, but fibres which do both. These are real ‘smart’ fibres. Historically, in technical textiles we have always been trying to protect, be it Gore-Tex, down clothing, or windproof fabrics.

We have been trying to reduce the impact of the surroundings on the wearer. This is borne of the ancient beliefs in the fear of outside, the alien, that the world is a threat.

In spacesuits, deep-sea diving suits, high altitude clothing, and polar expedition gear these assumptions might well be true. But in the everyday, even in potentially hostile environments like the mountains, perhaps we should be shifting to a position where fibres, fabrics and clothing are more about enhancing the interaction with the environment rather than limiting them. In practice, this means enhancing or amplifying the body’s exceptional thermoregulatory capacity, rather than limiting it.

Mess

On days like this you want to keep everything out, you want nothing getting in. Suit of armour, spacesuit, whatever. But these days are relatively unusual, and more often you want some degree with interaction with the environment.

Humans are extremely well adapted to prevent overheating. This is imperative, as while our core temperature can drop by more than 5 °C with no lasting effects, a rise in temperature of 5 °C is often fatal. Yet to survive the cold latitudes in which many of us live we wear clothing. This clothing protects against the cold, but it inhibits our most powerful thermoregulatory response: sweating. In effect we have replaced one evil – being too cold – with another: inhibition of cooling ourselves. And this is why fibres which thermoregulate, or enhance our ability to thermoregulate, are crucial.

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Why would you want to keep all this out? Smart materials and smart design let you interact when you want to, but keeps out the nasty stuff when you have to.

We don’t want a barrier, a suit of armour: we want something that allows us to interact with the environment.

If we go back to the early mountaineers they wore clothing which was mainly made from natural fibres such as silk and, particularly, wool. Their clothing allowed basic interaction with the environment. One way a material can interact is to be ‘smart’. Wool in particular seems a pretty smart fibre and adapts constantly to its environment: it has a huge heat of adsorption, greater than many of the manmade fibres which have been developed that boast smart properties. One can sometimes see steam coming from piles of sheared wool as rain falls. When worn, this latent heat is fantastic in that it can keep a user dry in damp conditions, but the problem comes if the user is overheating: they sweat into the wool and it gets hotter! That isn’t smart. Many of the ‘modern’ smart synthetic fibres boast the same properties.

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Another great example of interaction with an environment is an umbrella. The all-over Gore-Tex suit, less so.

There are plenty of other interesting limitations borne of the current ‘smart’ fibres. For example, wicking can prevent cooling: the body loses heat by sweat evaporating from the skin, and the greater the distance between the site of evaporation and the skin, the greater the reduction in sweating’s efficacy. This effect is magnified as the environmental temperature rises. Thus, wicking fibres which transport sweat far from the skin may well increase comfort by reducing chafing, reducing the feeling of skin wetness, etc., but they don’t necessarily aid thermoregulation. If used correctly, however, they can allow sweat to stay near to the skin, while spreading sweat over a large area and thus maximising cooling. This is an example where the fibre isn’t the key, but the ways that the fibres interact: this is fabric design.

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In environments like this, no one is thinking about the fibres or the polymers their clothes are made from: it’s all about the design of the garments themselves.

Much of the big talk over the last two years has been about air permeability and the resulting comfort.

This is a huge step in the right direction: it’s no longer about us versus the hostile environment; it’s about us interacting with it.

Air permeability, however, is not so much a fibre property as a fabric property. And fibres and fabrics are only a small part of the answer: a factor that makes textiles and performance clothing so exciting is the number of factors that influence performance. There are more hierarchical steps than in almost any other science. Polymers are the building blocks. There are more possibilities with polymers than we perhaps realise. We can change the polymer, the molecular weight, distribution, blends… there is so much potential. After that is the fibre. Old fibre production techniques still offer new possibilities, and relatively new fields like electrospinning are in such infancy that they offer near-limitless opportunities. Fibres go on to make fabrics, and here again are countless ways to innovate. Fabrics are where brands start to pay attention, and it their job to make sure they use the positive aspects of those fabrics to make garments which enhance those properties. The garments must also allow interaction with their environment and not merely try to barricade against it. Interaction with environment is the key to smart materials.

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Humans are amazing. We need to try to amplify our ability to thermoregulate, rather than shutting it off.

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Hot drinks in winter

It’s freezing here at Gearandmountains HQ: Leeds has suddenly got very cold. With this in mind, I’ve a topical post. It’s something I was asked a long while ago by a guy via email, and he wondered whether carrying a hot drink in winter had any real benefit. Surely it does? It’s hot, you’re cold – what’s not to like…?

It’s -10 °C, you’re in the Cairngorms. Only, you think you are, but it just so happens you can’t see anything because you’re in a whiteout. Your mate pulls something out of his bag. Haribo? Yes please. Free from Wiggle? Wow, they taste even better. Having gobbled the Haribo he offers you a hot flask. Free from Wiggle? No, not this time. However, oh wow that tastes good… but will it do you any good?

So, are hot drinks beneficial in the cold?

Google’s answer: I googled this conundrum to see what would come up and you get some entertainingly bad answers, such as “i was told a cold drink was better because it warms up inside you where a hot drink goes cold inside you”. This sort of justification does not get past peer review. So, more work required.

This guy could do with a hot drink. And possibly a facelift.

This guy could do with a hot drink. And possibly a facelift.

My short answer: if you go back to the basics, that thermal comfort is a state of mind, any psychological help (ie. stuff that makes you feel better) is beneficial. Therefore, I’d say if you enjoy drinking hot drinks then go for it. They can definitely feel reassuring.

My longer answer: From a physical point of view, to remain in thermal comfort you need to ensure you’ve no local cold spots, as well as a comfortable core temperature. If your throat, mouth, and lips, which are full of sensitive nerve endings, are cold then hot liquid on them will warm them up and feel good, unless you just burn them. There’s also research ( http://onlinelibrary.wiley.com/doi/10.1111/j.1748-1716.1973.tb05416.x/abstract) that shows that the extremities produce more heat when drinking a hot drink. Your hands and feet are full of nerves too, so warming your hands will definitely feel beneficial, especially if you need them to carry out dexterous tasks like unwrapping chocolate bars. Mmmm, chocolate. Anyway, first plus-point – hot drinks get rid of local cold spots.

From a core temperature point of view, liquid is required to keep your metabolic processes ticking over and ensuring you keep making heat, so consuming either a hot or cold drink is beneficial in cold conditions. However, the effect on core temperature of drinking a hot, as opposed to cold, liquid is negligible – there just isn’t enough liquid. You wouldn’t heat up a bath-full of water with a single kettle of boiling water, so you’ve no chance trying to heat up your 150 litre body with 1 litre of hot tea. It would have to be 1 litre of lava or something, and that is not very tasty. Just ask any geologist. Hypothermia is not recommended to be treated with hot drinks (“A warm drink will not provide a significant thermal benefit to the body. The most important ingredients in a drink are carbohydrate additives that will fuel continued shivering” from  http://onlinelibrary.wiley.com/doi/10.1046/j.1442-2026.2001.00172.x/pdf). This raises the other point that sugar (energy) intake is good for you when you’re cold. So, if you fill that flask full of seriously sugary gloop that’ll help you out. Mmmm, sugary gloop.

So, thus far we’ve seen that a hot drink will warm some sensitive areas like throat, mouth and hands, but its overall effect on core temperature will be minimal. However, as the short answer suggested, a massive effect is mental: do you like drinking hot drinks? If, like most Brits, you’re addicted to either tea or coffee, getting your fix on the hill will make you feel better (You wouldn’t send a crack addict up a hill without some crack (would you send them up there at all?)). Hot drinks are a great comforter, and therefore, come winter, they’ve a place in many walkers’ and climbers’ packs.

This enormous cornice caused us massive aggro. A nice hot drink would have been very welcome.

This enormous cornice caused us massive aggro. A nice hot drink would have been very welcome.

Pluses:

– Comforting

– Vehicle for sugary gloop and associated calories

– Opportunity to fuel caffeine addiction

-Warms cold and sensitive mouth and throat, plus your nose and chin if you spill it

Negatives:

– Faff

– Carrying a heavy and bulky flask

– No effect on core temperature

– Potential to burn yourself

Hot drinks are an essential part of any bivvy.

Hot drinks are a welcome part of any Alpine bivvy.

In conclusion, carry that hot flask if you think it will help – on this one, the psychological effects outweigh the physiological ones.

(Thanks to Dr M Morrissey, world-renowned thermal badboy, for his help on answering the original poser).