Hybrid base layer design creates three different zones that provide greater warmth where it is needed most, and greater breathability in the most critical area. The Tri-Tec Performance Base Layer Quarter-Zip combines our EST, MST, and LST base layer fabric weights in distinct temperate zones: - EST (5-ounce material) under arms and on wrists - MST (8-ounce material) on fronts of shoulders, forearms, and side/kidney areas - LST (10-ounce material) on torso and tops of arms
