Every trail runner knows that the temperatures can vary wildly in the mountains, so Salomon made the Trail Runner Warm midlayer with 4 way stretch, French terry, and added stretch panels and venting, so it's ready for cool mornings as an outer piece, or as a warm midlayer during winter runs. Provides warmth, the Advanced Skin Warm, 4 way Stretch Jersey fabric fights off morning chill so you can take your run higher. Provides breathability, because you really work up a sweat when you run, Salomon added venting panels under the arms. It's great as a winter midlayer under a shell, but a welded chest pocket and reflective details make it a pure running top as well. Material: Polyester, Elastodiene.