Hollow core doors are doors which are essentially hollow in the inside, save for some construction paper or cellular cardboard arranged in a honeycomb pattern. Doors are constructed with hollow cores as a light, cost effective alternative to solid core doors. These doors can easily be created in any style, and with certain panelling, veneers or styling, can easily be made to look like solid core doors. 

Hollow core doors normally feature a timber frame made out of pine, along with solid 'lock blocks' on either side of the door to allow a handle. The 'core' of the door is filled either with honeycomb. Depending on how it's constructed, this type of honeycomb reinforcement can provide a surprising amount of strength.The outside of the door is then finished with panelling, which helps to determine how the door looks, how well it insulates and how strong it is.