1. Kennedy RN. Handbook of foamed plastics. Libertyville: Lake Publishing, 1965.
2. McCurdy JL, DeLong CE. US Patent 2,669,751, 1954.
3. McCurdy JL, DeLong CE. US Patent 2,740,157, 1956.
4. Ingram AR, Fogel J. In: Frisch KC, Saunders JH, editors. Plastic foams, Part 2. New York: Dekker, 1973:525
5. Stahnecker E. German Patent 1,152,261, 1963.