Foamed paperboard is a composite material with applications in the consumer products industry. The composite comprises a layer of paperboard sandwiched between two polymer films. One film foams upon heating while the other acts as a barrier. Foaming is caused by the vaporization of the small amount of moisture present in the board. The resulting increase in pressure bubbles the heat-softened polymer. During growth, the vapor driving force, which depends on the rate of vaporization, overcomes the opposing sheet resistance. Upon continued heating, the vapor escapes through the molten polymer film and from the sides of the board. Less than 2% of the total initial moisture accumulates inside the foam. The average bubble size is about five times lower than the maximum possible bubble size because of moisture losses. The final bubble size and foam thickness are dictated by the degree of bubble coalescence.