The invention is directed to a composite foam material that is alkaline and heat resistance. The composite foam material comprises a foam layer that having a film layer attached thereto and in which at least one of the film or foam layers includes a carbon free radical scavenger agent that is dispersed therein. The carbon free radical scavengers neutralize free radicals that are generated in the polymeric material (e.g., film or foam layer) and help prevent the degradation of the foam composite material. In particular, foam composite materials in accordance with the present invention can be used in underlayment applications in which exposure to heat can degrade the underlayment. As a result, the durability and useful life of the composite sheet material can be extended. In some embodiments of the present invention provides a floor underlayment material that overcomes many of the problems discussed above.