This is 100% Yak, handspun by Eva. 2 ply, 103 g, 412 m.
Yak is very very soft, leaning to the Qiviut side of the spectrum. It is low in elasticity and this is quite a fine yarn so not one that would ordinarily be a candidate for a pair of socks. Of course that wouldn't stop me from trying ;o)
Here's what I came up with:
I knit a strand of fine lycra concurrently through the entire knit. (That's the cone sitting on the floor and if you squint you may be able to see the fine strand going up and through the right eyelet and feeding along with the yarn. The feed while unwinding of yarn and lycra cause a plying of the two to occur as they are drawn along.
Feeding on the left, you can see a small spool of Wooly Nylon. Initially I was going to run this through the entire sock, but at the last moment changed my mind and used it only on the heels and toes. This picture was taken while knitting the heel.
Here's another look, this time with the ribber removed (which I do just before knitting the toe).
Naturally I knit these for me.
Oops...ran short on toe of second sock. Finished off with a bit of Koigu.