I find if I wear wool and then put a wind proof layer over it, the wool will absorb sweat (which it does well) but then it will stay wet. If I wear all wool in whatever layers the temps call for, then the sweat keeps wicking out and dries off but I don't get cold. Wool lets the air filter through and that's why the sweat can dry, but it keeps you warm even when you can feel the air circulating through it. If you layer poly or wind-proof stuff over wool it traps the moisture in and doesn't let the wool do what it does best- which is circulate and vent out moisture and air while still keeping you warm.