Lightweight but warm down sleeping bag. "Rescue blankets" as a sleeping bag are not allowed, they do not breathe and the eternal crackle disturbs the necessary deep sleep (even your neighbors). An insulation mat is recommended as a base.
It is important to remember that the bivouac is at an altitude above 2000 m.ü.M. is pitched open and at this altitude during the night, even in the summer can be very cold!