For serious winter riding in all conditions, the Alpha Ultimate Insulated Jacket brings premium insulation to this do-everything-well jacket. Castelli's Alpha RoS 2 Jacket set a new standard in winter cycling comfort. The Alpha Ultimate Insulated takes that up a notch with stretchier fabrics and Alpha insulation that provides warmth without bulk. The jacket is lighter and more comfortable, with similar warmth and breathability. In fact, it's almost 30% lighter, with more stretch to feel even more comfortable. The fabrics make it possible. The fully waterproof and highly breathable Polartec® NeoShell® outer fabric has a high level of four-way stretch. This layer keeps wind and rain out while also letting sweat escape. The insulation is Polartec® Alpha® active insulation, which provides incredible warmth for its weight while also aiding in breathability. Fabrics alone don't make the jacket. The front has one zipper for the insulating layer and a separate zipper for the outer shell, so you can open the outside for ventilation while keeping the insulating layer closed. This allows for better overall ventilation during a climb or effort, yet you'll be drier when you close everything back up for the downhill. All the other features are carefully considered to make this your ultimate winter jacket.