By the third mile of a tempo run, the first-mile chill is gone and the On Weather Hybrid Jacket is still earning its place. On ThermaTec insulation keeps the core warm without bulk, and stretch panels around it let the arms and torso move freely. This insulated running jacket pairs the two panel types in one hybrid build. What Our Gearhead(R) Experts Are Saying:"Over several tempo runs that started cold and ended hard, I never reached for an extra layer under it and never felt the urge to peel it off by the last mile. I credit the lack of bulk, because nothing felt boxed in once the pace picked up. When the effort dropped for the cooldown, the warmth held steady instead of fading."