| http://www.w3.org/ns/prov#value | - In the mantle portion 16, the liquid center shell 20, and first and second mantle layers 22 and 40 are preferably made of elastomers, such as thermoset rubber, including polyisoprene, styrene butadiene, polybutadiene and combinations thereof, plastic, such as polypropylene; or thermoplastic elastomeric material such as copolymers of methyl-methacrylate with butadiene and styrene, copolymers of met
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