liner socks

I'd expect liner socks of similar thickness *and* density (i.e., tightness of the weave) to have similar warmth. A synthetic might dry out a bit quicker, but the wool will probably smell less offensive after several days of use.

I've often found that wool, even same thickness as synthetics, is warmer when wet. Perhaps something with the way the wool yarns are constructed (fuzzy)?

My impression is that wool (especially Merino wool) may have finer fibers than synthetics. Whether they are finer or not, body heat dries out a layer of these fibers next to your skin, even when the rest of the garment (or in this case your sock) is wet. This has insulating value, reducing conductive heat loss. Sounds scientific, no? I love Merino wool; it is the best. I like Possumdown (Merino wool & Possum fur fibers) even more because it is lighter, but it is not durable enough for hiking socks. It makes a great hat, however.

Possumdown!!?

I was at first surprised that light merino wool clothing is somewhat cool in warm conditions, different than what I expected. For example my BPL Beartooth Hoodie was much cooler than the BPL nylon thoroughfare shirt, and I sold the shirt because it was so hot.

The problem I see with thin merino socks is that they cost way more than thin liners or even nylon dress socks, and they wear out quickly… sometimes in just a few days. I have heard that overall, Darn Tough Socks wear well, but I would be more cautious of very thin ones if they make them.