Thermosetting polymers are a type of plastic that, once cured or hardened, cannot be remolded or reshaped. This process typically involves a chemical reaction that occurs when the polymer is heated or mixed with a hardening agent. As a result, these materials become rigid and stable, making them ideal for applications that require durability and resistance to heat. Common examples of thermosetting polymers include epoxy resins, phenolic resins, and polyurethanes. These materials are widely used in industries such as automotive, aerospace, and electronics due to their excellent mechanical properties and thermal stability.