Your mid-layer is the insulating part of your winter sports or outdoor clothing set, depending on the temperature you can play with it. If it is extremely cold, you can opt for a thick fleece cardigan or something with down.

If it is warmer you can put on a thinner second insulating layer. This also has to do with how much effort you are going to make.

If you are going for an active day, you will not have to wear a very thick second layer, but if you are going to drink beer all day on the terrace, you better put on a warm mid layer !;)