Collective term for substances with molecules of mostly varying size; these molecules are built up of so many identical or similar units (monomers) that increasing the number of units by 1 no longer makes any notable difference to the physical characteristics of these substances. Depending on the structure and crosslinking of the molecules a distinction is drawn between:

• Thermoplastics: linear or ramified molecular chains, but without interlinking
• Elastomers: molecular chains interlinked in a wide-mesh structure
• Thermosets: molecular chains interlinked in a close-mesh structure