Fleece tank over top. Do not confuse this base coat with another thinner Gore base coat. The only difference between the two is that this thicker version has a collar while the summer/spring underwear has no collar. Both have a wind resistant material that really makes this base layer better than others. Too bad Gore doesn't make a winter base coat for cold temperatures. I still go to Rahpa for a really warm base layer for cold weather. Rapha's winter baselayer includes a turtleneck and handguards with thumbholes. Now I have a complete set of base layers.