The Switch jacket by Mountain Equipment uses a combination of warm synthetic fiber fill on the body and stretchable fleece which allows a large range of movement. The Polartec Alpha used is a breathable synthetic fiber fill and lends itself to tours where insulation is needed, but the body is also required to work hard, for example ski touring. The fleece in the arms also retains heat but also offers more freedom of movement and increased comfort, which is a real advantage on the descent.
The tight fit ensures that heated air stays close to the body and cold air cant in the bottom. The flat seam construction prevents chafing, especially if you also have to carry a heavy backpack. Pockets offer plenty of space for equipment.
The Switch Jacket by Mountain Equipment offers warm insulation paired with good breathability.