A bivouac box for your backpack. A week bivouacking in Chamonix is about more than just boiling coffee and eating in your sleeping bag. When it comes to equipment, you need to make sure you are carrying only the bare essentials. As you will be packing your down jacket anyway, Mammut have developed the Sphere Eigerjoch sleeping bag. The volume of down, sourced from animal-friendly operations, is reduced in the upper body area to take account of the additional warmth provided by your jacket. To make sure you don’t need to leave your sleeping bag at all on very cold days or during bad weather, it has openings for the arms and a zipper at the bottom to allow you to walk around. An insulating collar retains heat around the feet while the closed hood combines an unrestricted view with effective protection from the cold.