Vulcanization is a process of hardening rubbers that involves the curing of elastomers. The term originally referred exclusively to the treatment of natural rubber with sulfur, which remains the most common practice. Vulcanization works by forming cross-links between sections of polymer chain, which results in increased rigidity and durability, as well as other changes in the mechanical and electrical properties of the material. Vulcanization is generally irreversible, and it is used to improve the lifespan, function, and strength of rubber products.

The most common vulcanizing methods depend on sulfur, which is a slow vulcanizing agent by itself and does not vulcanize synthetic polyolefins. Accelerated vulcanization is carried out using various compounds that modify the kinetics of crosslinking, and this mixture is often referred to as a cure package. The main polymers subjected to sulfur vulcanization are polyisoprene (natural rubber) and styrene-butadiene rubber (SBR), which are used for most street-vehicle tires.

Vulcanization techniques can vary, but they usually involve mixing crude rubber or other elastomeric materials with 5-30% sulfur or other agent with an activator, accelerator, and retarder to form a cross-linked molecular network. Vulcanization using sulfur alone is very slow and can lead to oxidative degradation, resulting in poor mechanical properties. This is why accelerators are added so that vulcanization can occur at a lower temperature and with greater efficiency. Vulcanization improves elasticity, hardness, tear strength, and resistance to organic solvents and abrasion.

There are many uses for vulcanized materials, some examples of which are rubber hoses, shoe soles, toys, erasers, hockey pucks, shock absorbers, conveyor belts, vibration mounts/dampers, insulation materials, tires, and bowling balls. Vulcanization revolutionized the way rubber is produced and how it can be applied. Before vulcanization was discovered, natural rubber was coagulated using acid and heat to make it malleable, but it would become brittle at low temperatures and melt at high temperatures. Vulcanization made rubber stronger and more elastic, and it is preferred by many manufacturing companies.