I get cold sitting, so wool if it's in the mid 30s or so, or if I'm still hunting or slow walking. Wool allows you to be quiet. Any lower than 30s I have the cabelas MT50 I think it was called, not sure if they have that anymore, but the wooltimate is also good. If you buy the good stuff it lasts a long time if you only wear it for hunting, unless you're dragging it through the nasty stuff, multiflora rose, barb wire fences, etc. My complaint with the synthetics is the noise against trees/brush. Fleece outer is a little better, wool is best in that aspect.