Cross-linking is a chemical process in which individual molecules are linked via bonds to form a network. Cross-linking is a key feature of plastics in particular, as its characteristics shape key material properties.
The degree of cross-linking is used as a criterion for dividing plastics into elastomers, thermosets and thermoplastics. Instead of directly during the synthesis of a plastic, cross-linking can also be brought about later by using a cross-linking agent.