I think it’s Tofutsies, and sadly, it is 50% wool, so that would be a no-go for someone who is allergic, as I am. One does have to be careful when looking at “Cotton” sock yarns, as they are often up to 50% or more wool, with just some cotton in them; Jawoll, Meilenweit, and Opal all make “cotton” sock yarns that are heavily wool-based.
I’ve just recently begun venturing into sock knitting - so far, I’ve completed a pair from Maizy, which came out very squishy and comfy. Little Knits carries a goodly number of the colors, among other e-tailers, and she also carries Panda Cotton, which was my most-recent and 2nd pair of socks. That’s another Classic Elite yarn, part cotton, part bamboo and part elastic, and is really quite beautiful, comes in nice prints and solids, and is super-silky (aka slides nicely on the needles, which Maizy did not!). I’m now just starting a pair from On Your Toes Bamboo, which is bamboo and elastic. Really nice stuff, but too soon to say much about it, other than it works up really soft and smooshy in 1x1 rib at the top of the sock - LOL! Once I finish those, I will be trying Kollage’s Luscious, which is another cotton sock yarn, a bit on the pricey side, and has been said to be very splitty by some knitters on ravelry - but the colorways are really nice, and the yarn feels pretty soft.
Other non-wool choices for socks include: Sockina from Schoeller and Stahl; Cascade Fixation, which comes in effects, spray-dyes, solids, and self-striping (but seems a bit pricey if you are knitting for larger feet!). I have also read that Elann.com’s Esprit yarn makes similar socks to the Fixation. Those are all cotton and elastic only.
Many people who are wool allergic or sensitive are also sensitive to mohair, angora, alpaca, etc. - basically, any animal fiber. Since I am not allergic to alpaca, I’m still searching for an appropriate alpaca sock yarn - one with some nylon/elastic in it to keep it from drooping. No such luck. Classic Elite makes Alpaca Sox, but that is 60/20/20 alpaca/wool/nylon. 