Because of frequent acceleration and slowing down and the high speed of most transportation systems, lightweight structural materials are needed to reduce their energy consumption while maintaining safety. Considering the extensive use of energy intensive transportation systems in the United States even a small increase in energy efficiency will result in significant energy savings and reduction in pollutant emissions. Closed-cell solid foams and microfoams are of particular interest since they are light and feature outstanding combination of mechanical, electrical, acoustic, and thermal properties.