Castelli Alpha ROS 2 Jacket Castelli’s warmest and most advanced jacket, the Alpha ROS 2 brings together warmth, breathability and weather protection in a single piece for ease of use and comfort when the temperatures are strictly single digit. Its close-fitting, racy cut is far nicer to ride in than a flappy windproof or waterproof jacket, and its one-stop weatherproof solution reduces the amount of mid-ride faffing as conditions change. The jacket uses a double layer construction to cleverly separate the insulation and protective fabrics for increased breathability and versatility. The outer fabric is Gore-Tex Infinium™ Windstopper® 150, which uses a breathable membrane to provide the weather resistance, and with the most exposed seams taped, it provides an effective barrier against all but the heaviest, most prolonged rain. Sewn into this, but separate at the front, is a grid fleece layer which provides extra insulation to the core whilst remaining hugely breathable. As the outer jacket and inner layer can be zipped up to different levels individually, the potential for balancing the precise level of warmth and airflow is huge and can be done without exposing bare skin or the base layer. When the Windstopper layer is unzipped, the rear vents also come into play for enhanced cooling. Castelli has also paid close attention to the details, with the double-cuff construction designed to provide an effective seal around gloves and the high collar keeping any chill off the neck. The stretchy waist and silicone grippers work to keep the jacket from riding up and to retain any warm air whilst still being flexible and unrestrictive.