Doors and paper honeycomb core Paper honeycomb core has been a popular filling material in doors for many years. Not only solid, but also moulded doors very commonly are filled with paper honeycomb core. Even fire retardant doors and steel doors are at times filled with paper honeycomb core, for this the paper honeycomb core has smaller cell sizes than for common internal doors. There are clear benefits to using paper honeycomb core as filling material for doors. Paper honeycomb core is packed and stored in a compressed state onto pallets. When used during production the paper honeycomb core is expanded to it's final form, generally some 10 times larger. The benefits of lower transportation costs and lower storage costs and space requirements are significant.