Wood is the traditional material for making doors, but solid wood doors require surface preparation and routine maintenance. They can also be expensive. Unless you have a specific reason for selecting an all-wood door, such as the restoration of a historic home, consider a maintenance-free steel or vinyl-clad door that comes ready to install in a variety of colors and finishes.

When buying a door, you'll need to specify a left or right-hand swing as well as an outswing or inswing door. To determine which version you'll need, imagine yourself standing inside the doorway with the door opening toward you. In that position, a left-hand door would have the knob on your left and a right-hand door would have the knob on your right.

Doors generally come in two types: exterior and interior. Swinging exterior doors are heavy and feature three hinges. They usually are made of solid wood or have a rigid frame filled with solid foam insulation that is covered by a steel skin -- sometimes called a steel door. Other types of exterior doors include sliding patio doors, hinged French doors, and storm doors. Interior doors are usually lightweight and require only two hinges for support. Flush-type doors are the least expensive. They are completely flat with hollow interiors that have a honeycomb grid of cardboard covered by a thin layer of finish plywood such as lauan. Panel doors are made of solid wood or a wood-fiber composition covered with vinyl cladding.