It can be both the second steel door or wooden.

Another problem in the “fight against cold” is a large convective heat transfer when opening the door for entering the house. It is possible to solve it only by installing the second “vestibule” door, creating an additional barrier to the penetration of cold air. It can be both the second steel door or wooden. The vestibule of two steel doors will increase the degree of protection of the room, but the inner wooden door gives great choice in design and has high thermal insulation properties. Therefore, the choice of a vestibule door is determined by purely personal preferences of the hosts.