Not only that, but they feel much better close to the body than those 1970s polyesters. This past summer, my husband, Bob, and I spent a few weeks testing some of these shirts, primarily to see how well they manage moisture. Most of the shirts we wore were lightweight and very breathable. They got damp but still felt comfortable. The biggest surprise was how light the shirts felt even when wet and how quickly they dried after we stopped running.
Some shirts are thicker than others.
You'll want to choose a shirt based on the conditions where you live and how easily you become chilled while running. Obviously, the heavier the underlayer, the warmer you'll be. But remember, you can become too warm running in a heavy base layer. Most lightweight shirts are sufficient for most runners in moderate winter conditions. Your shirt should fit snugly for maximum moisture management and warmth.