Which fabrics are best for which temperatures?

Heat retention of natural fibers, from best to worst (so you want poor heat retention --

go for something low on the list):

wool

silk

linen

cotton

(Kadolf, et al. 1993. Textiles, 7th ed. Macmillan)

This is a list of fibers, not fabrics--a closely woven fabric

of a "cool fiber" can be warmer than a not so closely woven

fabric of a "warmer fiber". A textured weave may be more

comfortable than a plain weave.

This is quite long, so please bear with me . . .

Which fabric you use to make your kit is going to be influenced not only by the weather and temperature, but also by the armour that you wear (or don't wear, as the case may be). A padded jack/gambeson/aketon is the equivalent of adding several layers of wool to your torso and upper arms, and you will need to take this into account if you wear one.

The fabrics that were used most frequently in the medieval period were wool and linen. Silk was an exceptionally expensive import, and was used sparingly as trim in most parts of Europe. Cotton makes occasional appearances in the Mediterranean area, but it was nowhere near as common as linen. It makes a decent linen substitute if you can't get linen.

Linen ranges in weight from something you can see through to a canvas-like material. It doesn't have good heat-retention properties, and thus tends to be quite a cool fabric. If you get wet in linen, you are likely to get chilled when you stop moving. Good for undertunics and warm-weather kit. Gets softer the more you wear and wash it. If you can't get hold of linen or it's too expensive for your budget, cotton makes a decent substitute. Good linen can be pricey, but keep a lookout for bargains.

Wool ranges in weight from something like a sturdy cotton right the way through to very thick and heavy. It has good heat-retention properties, even when wet, and will help keep you warm in the rain. Light wools make good cool-weather kit, heavier wools make good cold-weather kit, very heavy wools make good cloaks and may be water-resistant. Make sure you wash it thoroughly before making anything out of it, wool has a habit of shrinking! Often a bit pricey, but it lasts.

Silk also has good heat-retention properties, but it's expensive and sweat can stain it badly. Not usually worth the effort, except maybe as trim.

First case: fighting in armour. I fight in a mailshirt and associated gambeson, and find that even in a Scottish winter a linen undertunic and linen overtunic suffices on the top half of my body. I then wear either linen or woollen hose depending on the temperature. If I do start to get chilled when standing around, I can put on a woollen cloak, and add a woollen hood if my ears get chilly. If it's a really warm day and I start to overheat, I can take off my hose and run around with my legs bare under my knee-length tunic, just like they did a thousand years ago.

Second case: fighting as a 'squishy', without armour. Linen is good for hot days, light wool is good for cool days, thick heavy wool is good for cold days. If in doubt, layer! Nothing wrong with wearing a light woollen tunic over a linen tunic if you're not sure exactly how warm the weather will be. If it turns out warm, pull off the woollen tunic and leave the linen one on. If it turns out really warm, run around in just a linen undertunic. Ditto for hose: linen for warm days, wool for cold days, take them off if you get too hot. A linen hood can help keep the sun off on hot days, a woollen one helps keep the rain off on nasty days.

I hope this helps!