Polartec® Alpha® fabric is an excellent insulator, and it's soft, stretchy, and lightweight. A couple of years ago we thought it would be a great fabric for a base layer, but it tended to create a damp and clammy feeling on the skin. But when we were looking for more insulation for your sub-zero gravel rides we tried using Alpha® prototypes as a mid-layer over a Prosecco base layer, thus discovering the best combination for the cold. We worked on the details and created this mid-layer for riding in cold conditions. We added a half zip so it doesn't create bulk on the lower torso and we positioned it slightly off-center to avoid bulk on the neck caused by multiple zippers. We kept the fit snug so you can choose to tuck it into your bibs or leave it out as we do. We've also seen that it pairs well with a Flanders, Bandito, Miracolo, or Seamless base layer.