1. ASTM International: Standard Test Methods for Flexible Cellular Materials-Slab, Bonded, and Molded Urethane foams. D3574-03:3, Approved 10 July 2003
2. Gracovetsky, S., Farfan, H.: The optimum spine. Spine 11(6), 543–573 (1986)
3. Haex, B.: Back and Bed: Ergonomics Aspects of Sleeping, 1st edn. CRC Press, USA (1986)
4. Hill, R.: Aspects of invariance in solid mechanics. Adv. Appl. Mech. 18, 1–75 (1978)
5. Idzikowski, C.: Sleep position gives personality clue. BBC, UK (2003). http://news.bbc.co.uk/2/hi/health/3112170.stm , Accessed 16 Sep 2003