Solid Wood: Generally solid wood interior doors are six panel pine, but interior wood doors can be constructed from softwoods and/or hardwoods, such as mahogany, cherry, alder, maple, oak and pine. Solid wood doors must be maintained — stained or painted — on all surfaces as they will shrink and expand with changing humidity levels and temperatures in a building. With an STC of 35 to 40, solid wood doors will block most conversation sound transmission unless designed with glass inserts.
Medium Density Fiberboard: MDF is an engineered product of recycled wood fiber mixed with a resin and formed or molded into products, such as interior doors. The material is extremely stable and will not warp or shrink with changing temperatures or humidity levels. MDF does not have a grain and is easy to paint. Because doors are solid, MDF provides a similar weight to solid wood and STC levels of 32-35 (check with individual manufacturers).
Hollow Core: Constructed with a plywood or molded composite skin, these doors are hollow so sound and temperatures easily pass through. STC ratings vary but register as low as 20.
Solid Core: Constructed with a plywood or molded composite skin, these doors are filled between the skins with a wood fiber blend. STC ratings about 25-26 depending upon the filler blend.
Metal and Glass: In modern and contemporary homes, metal and glass doors are being used to accent the building’s style. Glass doors or inserts do not provide privacy, but when closing off heavy traffic areas or closets, they add character to the space. Steel doors, frequently used in commercial or industrial buildings, have high STC ratings of over 50.