The castelli alpha jacket is a superb winter jacket and demonstrates that maximum protection against the cold and wind doesn39t need to come in bulk the alpha uses a windstopper 150 fabric as the outer shell which is highly breathable windproof and water resistant with a 4 way stretch for great articulation we all know how important layering is in the winter time and so this castelli windproof jacket combines two garments in one by helping to regulate temperature while keeping bulk to a mi