After vulcanisation, rubber becomes

Poor quality rubber is made high quality this is done by heating with sulphur.  This process is based on creation of chemical and physical transverse bonds between rubber macromolecules resulting in a spatial vulcanizate mesh, giving unique properties to the material. Various chemical - vulcanizing - agents are used to create the chemical transverse bonds between rubber macromolecules (such as sulphur, peroxides, metal oxides, resins, quinones and others), which can react with appropriate functional rubber groups in the process of vulcanization