Wicking, yay, nay, or "it's relative" to the importance?

A lot of what Sumi describes about wool, ime, also applies to Flax/linen for hot weather, except that Linen wicks in a spreading way and is much cooler.  I love linen/flax for all but the most humid and hot conditions (tropical and near tropical).  Hard to find, but linen-synthetic blends are pretty good for those more extremely humid and hot conditions.

I do like wool-synthetic for colder weather.  I would love to try Alpaca-synthetic blend for cooler weather.

Cotton was mentioned several times here, and i get the sense that people don’t really understand why it’s such a poor insulator while wet and cold.

Cotton is actually fairly well insulating while dry.  Why?  The fibers are fairly small, and are like twisty ribbon structure which helps to still air better than a perfectly round fiber.

But a few things all contribute to it being a poor insulator while wet.  It’s not just about it “holding water”.  Wool also holds moisture, but is a decent insulator while damp.

First thing is that cool, twisty, ribbon structure tends to become flat when wet. Thus it loses some of it’s ability to still air and more of the conductive fabric touches the skin.  Cotton, a cellulose material, has higher conductivity than many other non cellulose fabrics–exception being nylon.  It swells a lot when wet, which decreases the interstice spaces between fibers, which further reduces it’s ability to trap air.  As mentioned, it absorbs and more importantly holds onto moisture a lot more than most other fabrics–even other cellulose based fabrics.  Some other cellulose based fabrics, also absorb a lot, or even more moisture than cotton, but because their physical structure is different, they also release moisture faster–like linen/hemp/ramie and tencel.

It’s a perfect storm of multiple factors and their confluence that makes it a poor fabric for especially next to skin wear in cool and wet, or cold and dry conditions.

It’s actually a decent outermost layer for very cold and dry conditions though, especially when waxed.