A number of thermoplastics have rubber-like properties. For more information, refer to ⇒TPE (thermoplastic elastomers). The historic differentiation between plastics (= thermoplastic) and elastomers (= crosslinked polymers) therefore is longer more valid. The term ‘rubber’, still refers to the group of cross-linked and thus non-thermoplastic natural rubbers (caoutchouc). Natural latex obtained from the trunks of the caoutchouc trees is another very important natural rubber. In addition, there are several types of synthetic rubbers with properties very similar to those of natural rubber (SBR = styrene butadiene rubber, NBR=nitrile butadiene rubber, ...). However, the properties of natural rubber are unparalleled in terms of its major characteristics, in particular long-term elasticity, cold elasticity and abrasion. Natural rubber consists of long-chain polymers (natural rubber made of polyisoprene with a molecular weight of 2,000,000). The monomers are not in a linear arrangement but comprise an obtuse angle. The rubber elasticity results in particular from the fact that these macromolecules are stretched by the application of force, but can completely return to their original position. However, the mechanical properties are considerably improved by crosslinking. The crosslinking by means of sulphur rings between the polymer chains, originally the only crosslinking used, is still significant but other crosslinking methods are used in addition today. As a rule, rubber has a high slide friction vis-à-vis almost all media. By means of plasma coating and by lubricant varnish, the sliding properties can be significantly improved. Furthermore, the sealing properties can be improved by hydrophobing. verbessert werden. Finally, items made of pure rubber do not look particularly attractive because rubber is brown by nature but mostly black due to carbon black stabilisation. By means of plasma treatment, the optical appearance of surfaces of rubber items can be enhanced.