I bought these (tops and bottoms) as a base layer for winter running in a cold climate. They are not thick, but the fleece side that touches your skin does feel warmer than just a regular polyester undershirt. It’s just one of multiple layers I’ll use depending on temperature. I never buy big name brand running clothes because years of experience tells me the material is what counts and nothing last forever. The only place name brands count for running is with the shoes.