I do find that 100% acrylic is warm also. Maybe it depends on the thickness? I have a thick 100% acrylic cardigan that is very warm. It is warm because it is a synthetic and does not breathe very well, so it traps your body heat. However, that can make some people (like me) sweat, so I don't generally wear it. Also, it is super staticky and does pill quite bad. I greatly prefer wool.