Base layers tend to fall into two camps: summer-weight pieces that barely register on the body, and winter-weight options that commit fully to insulation. The Endurance Thermobooster from Assos carves out a middle position for those transitional days and higher-output winter rides where you need warmth without the thermal commitment of their heavy insulation pieces. It's the base layer you reach for when conditions are cold enough to matter but your effort level means you'll be generating serious heat.

The construction centers on Assos's Sphere Ultra fabric across the torso, which uses a brushed interior face that traps warmth against your skin while the outer surface manages moisture transfer. Where the Thermobooster gets interesting is the strategic use of Type.613 mesh panels—these sit at the sides and across areas where heat buildup becomes a problem during sustained efforts. Rather than making the whole garment lighter or heavier, Assos maps different fabrics to different thermal needs across your body. The result is a base layer that holds warmth where you want it while venting where you need it.

Fit follows the close-to-skin principle that makes base layers actually function rather than just existing as another layer. The sleeves extend long enough to eliminate gaps at your wrists when you're in a riding position, and the torso length accounts for the forward lean that pulls standard shirts up at the back. A crew neck keeps things simple without the bulk of a collar interfering with your jersey's zipper.... Read More