polyester, wool, silk? which do you prefer?

[Cuffs]

You really want merino. Merino transports vapor away before it even becomes sweat droplets. Wicking fabrics (capilene and the like) only soak up moisture once it's come to droplet form. Hence the name wicking..,

http://us.icebreaker.com/Why-Icebrea...orm,en,pg.html

[JAK]

Wool even does a little better than that. When it is cold enough, some of the vapour leaving our bodies will condense, which releases the latent heat of evaporation. Even when we are not sweating this can represent 20% of our heat loss, which is recovered when we are wearing wool, when the fabric is cold enough. Then later when the fabric is warmer, like in the sun or shelter or when we are giving off more body heat, this moisture revapourizes, which using that available heat. So wool acts as a sort of thermal flywheel, being effectively 20% more insulating when we need it, and 20% less insulating when we don't.

You never want to wear too much, so that you are sweating, but if you do sweat now and then, like up a hill, wool can handle that quite well aslo, as long as you let it breathe and dry out again as you go back down the other side. When you really need alot of warmth you can wear a wind layer over the wool, such as when you are stopping for lunch or resting or exposed to wind. You have more time that you would with other fabrics because the wool can absorb up to 35% of its weight before it even feels damp. The moisture is there, in liquid form, but is spread very thin over the surface of the wool fibres. When you get moving again, or are warmed up enough, you can remove the wind layer and the wool will dry out again, and will be somewhat less insulating while it is doing so, as payback, but that's not really a problem because there will be times when you need more insulation and times when you need less.

[SassyWindsor]

Either polartec type or wool undergarments work great. I usually use older "moonstone" brand undergarmets which are dual layer synthetic. But sometimes I'll use smartwool, which I also love.

[Zipper]

Loved my patagonia merino wool long johns (#2 I think?) on my hike, but they were fragile and are now full of holes. I sewed up the holes in them several times. I now have some synthetic bottoms which have been plenty warm. I don't think I would worry about getting them wet as I would definitely have a rain pant layer.
Good luck with your decision!

[MissPak]

yeah but how weird would it be to come across someone in the middle of the trail fiddling with their crotch and then wiping stuff on their lips? o.O

oh god this was too funny!

[PinkRaven]

Wool or silk for your base layers. They don't hold stink the way synthetics do.
I like a thin icebreaker cami. I have some silk longjohns. Wool or cotton underwear. If you sweat a lot, go for the expensive wool undies. You want your girl stuff to be able to breathe.
For your outer layers, I recommend a fleece, a down vest, a packable down jacket and a high quality breathable shell. I don't like any of my individual layers to be too think.
The "high-tech" synthetics, from my experience, are overpriced and overrated.
PinkRaven