1. Morehouse, D. S. J.; Tetreault, R. J. U.S. Patent No. 3,615,972,1971.
2. Synthesis and properties of thermoplastic expandable microspheres: The relation between crosslinking density and expandable property
3. Sack, W. H. U.S. Patent No. 4,133,688,1979.
4. Duris, T.; Mobbach, R.; Riethues, M.; Renz, G.; Jacob, D. U.S. Patent No. 20060057291,2006.
5. Sato, H. Japanese Patent No. JP 2006291137,2006.