What are the different door cores available from most manufacturers, and how do I select the best type for my application?

Steel doors are differentiated by their core, with each type having a different set of properties and performance characteristics. The five most common cores are honeycomb, polystyrene, polyurethane, steel stiffened, and temperature rise. A honeycomb core door is used for interior and exterior openings where high thermal insulation is not required. Polystyrene core doors are the most commonly specified insulated core and are suitable for applications requiring an R or U factor (a measure of insulating performance). Polyurethane core doors provide superior insulating properties and are suitable for exterior openings in cold climates. Steel stiffened core doors feature steel ribs in the interior of the door and are ideal for high traffic, non-aesthetic applications. Temperature rise core doors are used when a fire resistance rating is required to retard the transfer of heat from one area to another (a stairwell, for instance).