What Our Gearhead(R) Experts Are Saying: "This layer surprised me-it's insanely warm for how thin it feels, and it packs down just like a rain shell. I use it as a jersey in shoulder seasons and a midlayer when it gets seriously cold. The second-skin fit plays really well under outer shells without bunching."From frosty fall mornings to midwinter base miles, the Endurance ThermoBooster Top delivers the perfect thermal balance for high-output rides. Engineered with the soft, brushed Skuba textile and a racingFit silhouette, this layer feels like a second skin-warm, breathable, and low-profile enough to disappear under your outer shell. We love how it regulates temperature whether we're climbing in the cold or holding tempo into the wind, and when things heat up, it packs down small enough to stash in a jersey pocket. It features subtle, rider-ready details like a comfort-fit struzzoKragen collar, dual rear storage pockets, and raw-cut edges that layer cleanly under gloves and jackets. Whether worn as a standalone top or slipped beneath a shell, this is our year-round layering essential when temps are low and the pace is high.