This pet door consists of a heavy-duty aluminum frame with a ¼ inch, aluminum-lined Plexiglas flap. The flap is lined with a high-quality nylon pile-brush material which aids in the sealing of the pet door. The unique feature of this pet door is the aluminum-lined, Plexiglas pet flap. This feature protects the flap from biting behaviors that often are found in kennels. This door is designed to be surface mounted; however, there is an option to have exterior frame pieces. Typically these pieces are not needed for the installation of the pet door, but they are available. Please call Moore Pet Supplies with any questions at 1-800-829-7876.