These are mostly acrylic, an important characteristic of acrylic is that it does not absorb moisture well. However, it is able to wick moisture from the skin (which is what you want when exercising); producing less moisture at the skin surface lowers chance of blistering than do cotton socks. For exercising, if you must go cheap on socks this is the way to go; polyester is sufficient as well.  But in the end you cant beat the coolmax based fabric.

I use these as cheap alternative to my coolmax for my Vibram's if they are dirty or just for walking around in (however the fabric is pretty loosely stitched so without something underneath them they will wear out very quickly I imagine).

By the way, these socks are crew length, so they should come midway between your ankle and calve.