1. Solidgold Helmet Sdn. Bhd. Malaysia, 1999, private communications.
2. H. Hartung, Method for producing a protective helmet, US Patent 4288268 (1981), to Intellectual Property Network, IBM.
3. Fast fracture of rubber-toughened thermoplastic used for the shells of motorcycle helmets;Gilchrist;J. Mater. Sci.,1987
4. J. Gessalin, Safety helmet with a shell injected from thermoplastics and method for the manufacture of said helmet, US Patent 4466138 (1981), to Intellectual Property Network, IBM.
5. K.V. Sibley, E. Ponzer, Method for producing a protective helmet, US Patent 5298208 (1994), to Intellectual Property Network, IBM.