The establishing of chemical links between the molecular chains in polymers.
When extensive, as in most thermosetting resins, cross-linking makes one infusible super-molecule of all the chains forming a three-dimensional or network polymer, generally by covalent bonding.
Thermosetting materials cross-link under the influence of heat and/or catalysis, irradiation with high-energy electron beams, or chemical cross-linking agents, such as organic peroxides