I would say wool, but it isn't wool 
My local Sainsburys seems to be selling off a lot of the Red Heart yarn really cheap. I got some nice bright pink with a sparkly thread through it for I think 1.19/100g instead of 2.99, 89p/100g for plain plum colour, and about the same for plain baby blue. All dk, all acrylic but it looks ok for everyday stuff.
It was way overpriced for acrylic to start with so I haven't actually tried it before, but worth a go. It doesn't feel as nice as Stylecraft Special but feels nicer than Robin, IYKWIM.