These could also be called "reclaimed children's tights" since they are made out of do it yourself craft loops. I had some tights that were no longer needed (one had a communion stain on the knee), so I tried this. Simply cut strips across the legs (of cotton tights) about 1/2" wide, link them up and roll into a ball. I used size 13 knitting needles, cast on 15 stitches and worked in a basic garter stitch until the size seemed right. While they are definitely primitive, I like them. They also work very effectively, and the texture is nice.
p.s. T-shirts, knit pants, knit pillowcases, or anything that can be cut into loops works fine for this. Experiment!