My neighbour used the same technique to built his house here in Germany together with his wife. Their house know fullfils the requirements for one of the highes

My neighbour used the same technique to built his house here in Germany together with his wife. Their house know fullfils the requirements for one of the highest insulation standards here in Germany, called "Passive House". So I assume there must be great insulation materials available that can be attached to the outside of the walls.