I went on a five mile hike yesterday in Shenandoah National Park along 2 rivers. Did not get over 40 degrees, colder on the shade side. The jacket kept me warm. There were some rough inclines/declines and going over and under down trees and the jacket stretched perfectly for me to maneuver around these trees without feeling it was tight on me. I'm 5'3, 125 lbs. I bought the small. The sleeves are about 2 inches too long, though. That's my only complain. Other than that, I love the jacket.