Sheree's advice on what makes a good sock yarn
Yarn does not have to be labeled
"sock yarn" to be used to produce perfectly wonderful socks. Ideally,
it needs to be of a weight and style so that it will be appropriate for socks
(fingering weight is fine, sports yarn is fine,
baby yarn is fine, worsted weight is fine, as are many of the other weights and types of yarn). I have produced socks to be used as slippers from bulky yarn, but they sometimes turn out too dense and solid (the socks as body armor syndrome). There are certain fibers or combinations of fibers that work better than others. Generally, anything that will mat or felt up when it is worn isn't desirable (unless you're making felted slippers or the like). Generally, yarn without any stretch or give to it doesn't work too well, because then you have trouble getting the sock on your foot over your heel, and once it is on, the top won't stay up. Generally, yarn with some nylon or other synthetic content works well, because the synthetic helps the wool to wear better on heels and toes. Generally all synthetic yarn (acrylic or the like) is not desirable because it produces socks which are cold in the winter and damp and clammy in the summer (synthetics don't have the wicking action that wool does). Sometimes it is possible to combine various fibers and types of yarns to overcome their shortcomings and capitalize on their benefits. For instance, I have made beautiful socks from some handspun and hand-dyed wool yarn plied along with a thinner acrylic yarn from my stash. Neither yarn is labeled "sock yarn" but the two combined are thick enough to knit up easily, not so thick that they are revoltingly dense, the acrylic content makes them wear well, the wool content makes them comfortable to wear, and they handwash like a dream. Probably many of the yarns already in your stash can be used to knit wonderful socks, with some swatching and careful label reading.