Foamed paperboard is a composite material with applications in the consumer products industry. The composite is comprised of paperboard sandwiched between two layers of polymers. One layer foams upon heating while the other acts as a barrier layer. Foaming is caused by the vaporization of the small amount of moisture present in the board and the resulting increase in pressure. The mechanism of foaming was investigated with a combination of high-speed photography, scanning electron microscopy, and infrared thermography using foamed paperboard of different compositions prepared both in the laboratory and on a commercial machine. The surface uniformity of the paper was found to be the overriding paper-related property controlling bubble formation. (c) 2007 American Institute of Chemical Engineers.