sam4797668 wrote an answer about Marmot Tamarack Pant - Men's on November 28, 2013
In zero degree weather you need to insulate with layers. This is an outer shell layer and should not be used as a baselayer or mid layer. It's job is to shed wind and moisture. So to directly answer your question, they will keep you warm as part of a layering system. If you wear these and skivees alone you will get cold instantly.