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Why is sulfur heated with rubber during vulcanization?

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truck tires being removed from their molds — rubber Truck tires being removed from their molds.

Sulfur is heated with rubber during the process of vulcanization to chemically alter its physical properties, transforming it into a more durable material.12

When heated, the sulfur reacts with the rubber to form cross-links, or bridges, between the long-chain polymer molecules. These cross-links provide several critical improvements:12

Enhanced Strength: The material gains higher tensile strength and increased resistance to abrasion.1
Improved Stability: The rubber becomes more resistant to swelling and maintains its integrity across a wider range of temperatures.12
Elasticity: The process ensures the rubber retains its essential elastic properties while becoming more stable.2

While the exact chemical reactions are complex, this bonding process—discovered by Charles Goodyear—is fundamental to creating the durable rubber products used in modern industry.1