"Max, you're wrong. Wool dries slowly which reduces flash cooling, hence the "warm when wet"."
There's more to it than that, if it was as simple as the above, then any hydrophillic and slower drying material would have some "warmth while wet" properties, and that's just not true.
Cotton for example, even my beloved, hollow core fiber Linen isn't warm when wet, in fact, it's quite cooling though it will feel drier longer and faster than will cotton.
There's different things at play here. The conductivity of the material seems to matter, and to some extent the physical structure.
Wool was designed by nature to provide some warmth while wet, and sheeps wool along with some other animal fibers are somewhat uniquely designed in that respect. So no, Max isn't far off on this one (though i think it's often exaggerated a lot). However, they would be even warmer while wet if one could keep them in their natural state (as on the animal), more filled with waxy or fatty coatings that also provide water repellency.
My ancestors, the Scottish Highlanders, wore a lot of very greasy wool in a climate that tends to be cold, wet, and windy (and use to be noticeably colder in some semi-recent cycles, like the mid 1700's or so). It was their primary garment material (not so well known, is Scots also often wore linen)
If wool wasn't warm when wet, they would likely not have survived that crappy combination of conditions. In some ways, such conditions can be more challenging than extreme Arctic, but dry cold.
