What makes some clothing materials “warm when wet” (like wool) but others not (cotton)?

Question

What makes some clothing materials “warm when wet” (like wool) but others not (cotton)?

In: Chemistry

Answer 1

Going from memory of what I learned in Boy Scouts in the 1970s, wool fibers are hollow and naturally insulating because of the dead air space inside. Plus, they don’t absorb water like cotton, the water just sits on the surface and can easily evaporate. Water inside the cotton fibers takes forever to evaporate and conducts heat away from your body while it’s in there.
Here’s an experiment: find a wool sweater and a cotton sweatshirt of similar size and weight. Weigh them dry and then wet. The cotton garment will gain massively more weight by proportion, and is heavier even after you’ve wrung it out.