It consists of polybutadiene, an elastomer (elastic polymer) built up by chemically linking multiple molecules of butadiene to form giant molecules, or polymers. The polymer is noted for its high resistance to abrasion, low heat buildup, and resistance to cracking.

Butadiene (CH₂=CH―CH=CH₂) is produced by the dehydrogenation of butene or butane or by the cracking of petroleum distillates. It is polymerized to polybutadiene by solution methods, using anionic or Ziegler-Natta initiators. Like the other diene polymers, polybutadiene is isomeric—it can be…

Polystyrene and polybutadiene are incompatible, so that the polystyrene end-groups associate together to form domains of glassy polystyrene in a sea of elastic polybutadiene. The polybutadiene centre portions thus form a connected elastomeric network held together by rigid domains of polystyrene end-blocks, which are relatively stable up…