Wooden doors are made from either affordable softwoods or, at the higher-end, more durable and elegant hardwoods. Both interior and exterior doors are made from a variety of materials, color, strength, density and hardness. A flush door is a completely smooth door, having plywood or MDF fixed over a light timber frame. Several of these woods include Redwood, Douglas fir, Maple, Poplar, Pine and Oak. Each type of wood has its own sub species as well. Available in different thickness, sizes and brands.