Which natural (non-synthetic) fabrics are good for hiking winter weather? I know cotton will generally trap moisture and invite hypothermia, while wool is warm but heavy. What other natural fabrics will work well in winter conditions?
There are many excellent natural fabrics for winter hiking:
- Merino wool is often used as a baselayer but I have also found silk and bamboo to be very good.
- I have a knitted raw silk midlayer but also like cashmere, which is warm, light, doesn't smell and releases moisture pretty well.
- In colder conditions I wear sweaters made of untreated wool (Black Welsh and Herdwick). They retain their natural oils and are really warm but a bit heavy and itchy if they touch your skin.
- My favourite natural fabric for hill-walking (I live in the Pyrenees) is Pyrenean wool. It is fluffy and quite light, being soft-ish wool on a cotton matrix. I have never seen it in England but it's very popular in France. I have a gilet made from it that is several years old and still going strong.
- My Black welsh sweater by the way is over thirty years old (been repaired a few times but unbelievably bullet-proof).
When I'm enjoying nature I like to wear what's natural.
You probably want wool. Wool has a fairly good warmth to weight ratio, and keeps most of its warmth when its wet. You can get wool products for both base layers and insulating middle layers. "Merino wool" is the style of wool that seems to be popular for high end outdoor wear now.
They can be expensive, but the following companies make very high quality wool pieces for outdoor wear: Ibex, Smart Wool, Icebreaker. More general outdoor companies like Patagonia, Arc'Teryx, and Outdoor Research also offer some wool pieces. Unfortunatly, they're very expensive. Like a lot of "natural" products, wool outdoor pieces are priced as luxury versions of the synthetic ones.
Down may also be appropriate, but I've never seen down jackets that weren't also made with nylon (I don't understand your motivations for wanting natural materials, so I don't know if this is a problem). Down has the best warmth-to-weight ratio of almost any material, but keep in mind that its worthless when it gets wet.
For what its worth, wool is relatively warm when its wet, but that isn't a substitute for keeping dry - if it might be raining where you're going, you should bring some kind of dry outer shell. Unfortunately I'm not aware of any commercially available natural materials for that (i.e., there isn't a natural alternative to a Gor-Tex jacket). Even with nice wool layers, if you get rained on enough, you would still get hypothermic.
As others have said, wool is the best of the easily available natural materials. It's main advantages are:
- Somewhat hydrophobic, in other words is a little bit water repellent. This is due to wool fibers being hollow with some fat inside. This fat inside is also the reason you should never wash wool in ordinary detergent. It will wash out the fat, which changes the wool's properties and also makes it shrink.
- Retains a significant fraction of its insulating power when wet. It is not as good as the best synthetics at this, like polypropelene, but it's lots better than water absorbing fibers like cotton.
- Much of the water can be wrung out. The wool will feel noticably less wet after this, more damp than wet. Cotton, in contrast, will still be wet after wringing it out.
On the downside:
- Fairly heavy for the insulation value.
- Some people are bothered by the "scratchy" feel of the fibers and can't tolerate having rough wool, like a sweater, right up against their skin.
- Not very wind-tight. There are some wool sweaters that are fairly wind-tight, but they are also exceptionally heavy.
- Needs special care to keep clean. You can't just throw it in a washing machine with normal cotton clothes.
Down is a very warm natural material and is highly compressible, but has serious downsides that it looses most of its insulating property when wet, and it really soaks up water and not only stops insulating but gets very heavy. For most people that go places often enough where getting rained on is a common consideration, down is essentially useless for clothing. Down can be good for something like a sleeping bag that you have means to keep out of the rain.
There are other natural materials with some interesting properties, but after wool and down they get exotic, and either impossible to find or very expensive if you do. For example, wolf fur is the best for repelling snow, and seal skin is particularly good for waterproof garments.
I know you asked about natural materials, but without explaining why your question is limited that seems silly. Modern technology has not only produced materials that are very good for outdoor use, but has also made them accessible and affordable. For example, polypropelene is even better at insulating when wet than wool, and feels much more comfortable against your skin. A tight nylon mesh is still breathable but much better as a wind barrier for the weight than any natural material I know.
My winter outfit uses a combination of materials. Cotton is no good when wet, but light and comfortable when dry. When you know you can stay dry (which includes managing sweat), cotton can be nice, but be prepared to change quickly when conditions change. For serious conditions I like a polypro "sweater" on first, a wool sweater over that, and a wind shell over that. The wind shell can be a ordinary windbreaker (preferably without extra insulting lining, just a real windbreaker) or a rain shell, depending on conditions. You can mix and match these layers to suite a variety of conditions.
In winter particularly, be aggressive about changing your layers for the conditions. You're going to get hot hiking uphill. Strip down as appropriate as soon as that happens. As soon as you get to the top, put on a layer or two before you cool down. It's a lot more comfortable to switch layers when you're warm.
Sheep's wool, especially the comercially sold hiking variants like Icebreaker*, is the least warm options out of all standard wools. If it has to be sheep's wool, take homeknit, from feltable wool. A cable design will be warmer, since it has more wool in the same size. But it is probably better to look into other animals.
If you are on a budget, I would suggest alpaca, which is much warmer at the same thickness. The downside is that it is also much heavier. Llama performs basically the same as alpaca, but is rarer to find, so not worth chasing. Camel is good. A better, very light choice would be cashmere, which fluffs up to considerable warmth even at thin weights. But the one that beats them all is the yak. Get a yak sweater if you want to stay really warm.
Other wools will not give you anything special for hiking. If you can even get mohair in thick gauges, it won't be warmer than sheep. Angora is OK, but not better in warmth, weight, price or user friendliness. Some absolute exotics like vicuna are expensive because of their rarity, I haven't tried them, but I can't imagine their functionality being proportionate to their price tag.
Silk is not really warm. It can create a good underlayer, but it's closer to standard polyester in its qualities, more likely to make you sweat than to keep you tempered.
Stay away from the usual plant based fabrics - cotton, kapok, linnen, ramie and juta. None of them provides good warmth or wet performance. Also don't use synthetics, including all kinds of acetate, viscose, milk and soy, even if the label says "natural"**. Without going into philosophical discussions about natural vs. nonnatural, they are not as warm as the other materials I discuss here.
Leathers won't warm you per se, but they will keep wind out, which is quite valuable. They can make a decent outer layer, but most people nowadays would choose other options.
The outermost layer I would suggest is not leather, but something filled with down. It is not strictly fabric, but you cannot beat down for insulation, not with artificial fabrics nor with other natural materials.
A last paragraph: you say "wool is heavier". If the weight of sheep's wool is already a concern for you, I assume that you either have not tried it (and so are not familiar with natural fabrics) or are looking for something that is just like artificial or synthetic fabric, just warmer. To make it perfectly clear: such a beast doesn't exist. Natural fabrics are very different in weight, body climate, washing, drying, coloring, and skin feel. Before you invest too much money, make sure you know what you get and that you can live with its downsides.
* This is not just a general "handmade is always better" snob attitude. First, they tend to use rather thin fabric as opposed to rustically knitted clothes. Second, they almost always sell machine washable nonitchy wool, which is made by removing the microscopic hairs sticking out of raw wool. Sadly, these samie hairs are great at trapping additional air, making traditionally processed wool much warmer at the same yarn weight.
** Nowadays marketing loves to call them "natural", as in "natural bamboo socks" but the standard terminology is to use "artificial" for anything made from oil, "synthetic" for fabrics which have been chemically synthesized from natural materials, and "natural" for fabrics created with non-chemical processing of natural materials.