This is a "sock blank", I bought it from Sock Blanks, from Sidney on etsy, it is sock yarn machine knitted into a rectangle, like a short scarf, with two strands of yarn held together. It is then dyed, in this case in this fantastic green and black pattern. With this you knit socks just by unraveling the edge. It is a marvellous invention!
Sockor (socks in Swedish) and can be found in "Regiahäfte nr 2". I know it is fun to knit socks with all kinds of patterns and colours, I have been there to, but for comfort and wearability, this is the sock!