Which Interior and Exterior Door Materials Are Most Durable?

There's more to doors than wood and hardware. Doors are often made with special materials and reinforcements that enable them to stand up to the elements and everyday life. But not all are created equal: The way your doors are constructed could affect how well they work and how long they last. Learn everything you need to know about interior and exterior doors to help you figure out which type is right for your home.

Exterior Doors

Because wood has a tendency to warp as it expands and contracts with the weather, a door can't be made from a single slab of wood. Centuries of experience have resulted in the practice of making doors from interlocking pieces. On a panel door, you can see the rails, stiles, and panels. But even flush doors—those built with sheeting like MDF or plywood—have frames and fill-in pieces, all covered by a solid piece of veneer. Not surprisingly, some door materials perform better than others. Check a door's construction to make sure it will meet your needs.

• Solid-core flush exterior doors are made much like hollow-core interior doors, but the space within the wood frame is filled with solid particleboard. These are very heavy but not as durable as other exterior doors. Without the protection of paint, the veneer may delaminate from the particleboard. And if the particleboard gets wet, the door can become unusable.
• Fiberglass exterior doors are quickly gaining in popularity. Fiberglass is easily molded into almost any shape and style, and it's also durable, hard, and resistant to shrinking, expanding, or warping. These doors are available in a variety of colors and are easy to paint.
• Wood-panel doors, made for interior and exterior applications, have a classic appeal. Solid wood brings impressive strength and insulating properties. Hardwoods such as oak are very resistant to denting; softwoods such as pine are more easily dinged but are still quite durable. You'll pay more for a stain-grade door, which is made of full-length, attractive pieces of wood. A paint-grade door joins together smaller pieces and is less expensive. All exterior doors must be protected with paint or finish to prevent them from warping or cracking. Some exterior wood-panel doors have a foam core for added insulation and stability.

• Stave-core exterior doors (also called "core-block") look like standard wood-panel doors, but they're actually made from several thin pieces of wood laminated together. The laminated core is then covered with wood veneer. This method makes for an extremely stable door. However, the veneer is liable to peel if the door is not protected with stain or paint.
• Steel exterior doors were once considered an option only for commercial applications, but they're now increasingly popular for homes. Some have a steel face with a foam core for insulation. Others have a core made of foam wrapped in steel with a layer of wood veneer applied to the exterior. The result is a highly insulated door that's also very strong and burglar-resistant.

Interior Doors

Interior doors aren't exposed to the elements, so they can be made of less substantial materials than exterior doors. Can you use an interior door as an exterior door? No—regardless of how well you protect the door with paint, it will warp and come apart in a few years.

• Hollow-core flush interior doors are a common choice for new construction. These have a frame made of solid wood boards that are typically about 1-½ inches wide. A cardboard webbing runs through the interior to provide rigidity and prevent drumming. These doors can last for decades if treated gently, but they can be dented or punctured if hit hard. Hollow-core doors with lauan mahogany veneer are the least expensive but will soak up paint like a sponge. It often pays, in the long run, to buy a door with oak or birch veneer.
• Stamped hardboard interior doors are often the most affordable choice. The hardboard (sometimes called by the brand name Masonite) is fairly soft compared to other door materials, but it is usually covered with hard-baked paint and molded into a convincing imitation of natural wood grain. Some hardboard doors are hollow-core, while others are filled with foam or particleboard. These can look great for years if treated gently, but they are easily dented; if they become wet for prolonged periods, the hardboard will swell. Both conditions are difficult to repair.
• Medium-density fiberboard (MDF) interior doors are gaining in popularity. These doors are available in a wide range of attractive styles, including many with a paneled yet modern look. MDF is harder and less susceptible to denting than hardboard, though not as strong as solid wood.

Glass Doors

Glass-paneled doors need to be well-built, especially if they are being used as exterior doors. Individual glass panes are often referred to as "lights" (or "lites"). Be sure to choose gas-filled thermal glass panes, which add insulation, for an exterior door, and confirm that the glass is well-sealed against the stiles and rails.