Here are the different types of doors in the Universe:

Oak

Maple

Pine

Cedar

Fras

Steel

Glass

Obviously this story centers around the Pine doors.  Here are some facts about Pine doors:

Pine doors are crafted for traversing the dimensional plane. Pine although easy to work with for practical purposes is tricky for inter-dimensional purposes. Age of the pine, preparation and grain all determine the depth in to the dimensional field. Design and Creation of a Pine doorway is only taught to Masters by appointment from the Architects Council.

Enjoy!