They are a base layer. I thought I covered why I wore an UA shirt under them quite well. I dont always wear UA under them. IF, I want a mock T neck I do. However, these are WAY too warm to wear until it gets COLD out.. If I could buy them with a mock T I would throw my UA away.. I will wear them straight under my camo.. nothing over them most of the time. Once it gets real cold, I throw another layer over them.
Trust me, they work well. Tree stands get cold.. But you havent felt cold in central ohio until you put on a cop uniform and direct traffic at a wreck for a couple hours in the wind and snow or rain..