This can be any form of mid-weight top layer to give a bit of extra warmth on Mont Blanc itself or to use on its own when the main fleece is a bit too hot. It should be roughly half the thickness of your main fleece layer, and could also take the form of a thinly insulated "soft shell" style garment, which has the big advantage of working as a windproof outside layer on it's own.
Suitable models: any mid-weight insulating layer, or soft shells (non-membrane) such as Marmot DriClime Windshirt or Paramo Quito jacket, both of which are excellent.
Quantity: 1