What Our Gearhead(R) Experts Are Saying:"The Cold Days 2nd Baselayer slotted right between my Flanders base layer and my winter jacket and made a noticeable difference on a ride that dipped below twenty degrees. The Polartec Alpha fabric added real warmth without the clammy feeling I usually get from heavier base layers, and the off-center half zip kept bulk away from my other zipper pulls."The Cold Days 2nd Baselayer from Castelli was born out of a specific problem: needing more insulation than a base layer alone can deliver on sub-freezing rides without the bulk of a second jacket. Polartec Alpha fabric brings soft, stretchy, lightweight insulation that layers cleanly between a base layer and an outer jacket. The off-center half zip keeps everything streamlined at the chest, where zipper bulk tends to stack up most.