A frosty pre-dawn training ride on empty roads calls for a warm layer that stays slim, and the Thermal Base Layer is a low-profile thermal base layer for cold weather training. A classic crew neck streamlines layering under a jersey and jacket. What Our Gearhead(R) Experts Are Saying:"On hard intervals under a cold grey sky, the soft, textured fabric and flat-locked seams felt smooth against my skin from the first effort to the last. I stopped noticing the layer, so the session stayed about the effort."