Unlimited design possibilities exist with Flush Doors. Built like a sandwich, Flush Doors allow you to build just about any type of design, creating infinite personality for your doors. Starting with a solid fir frame for strength and durability, polystyrene insulation is placed into the middle and Lauan plywood is added to the back. Then, from your design, the facing and trim material is fitted and attached to the face of the door, providing the distinct beauty you desire.