Thumb holes keep the sleeves from shifting or flapping in the wind and add a little more coverage in cool weather/ morning running Back zip pocket provides secure storage for esstenial stuff—like cards and keys Four-way stretch fabric, buttery soft, naturally brethable and sweat-wicking fabric keeps you dry and comfy Slim fit layers easily under jackets and delivers a sleek, more feminine silhouette Great choice for training,climbing hiking and other workout 91%Polyamide,9%Spandex, NWOT