What kind of yarn should I use for warm winter socks?

Dear users, dear authors,
What kind of yarn do you use for warm winter socks?

When it comes to winter socks, I look for a high percentage of virgin wool. That means I have to wash the socks by hand, but I’m happy to do that—especially since I don’t use detergent on my socks; instead, I use shampoo, which keeps the wool fibers soft and supple.

Yes, I also look for a high wool content in socks. I’ve used pure virgin wool several times now and notice that the socks are very durable and stay clean for a long time. 

All my wool socks can go in the washing machine, but only on the wool cycle and with shampoo.