Cozy baselayer or lightweight insulation piece? You get both with the Descente Mathias Mid Layer Top This technical layer can be worn either next to skin or over another baselayer depending on the weather The Mathias Top is from soft touch Supplex fabric that?s cozy and warm It also breathes and wicks moisture to keep you comfy during aerobic activity Supplex synthetic fabric Breathable and moisture wicking to keep you comfortable during activity 1/4 zip for easy on/off Regular fit is relaxed but not too baggy Average center back length measures 26