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, causing it to form a rigid structure. Common examples include epoxy resins and phenolic resins, which are widely used in adhesives, coatings, and composite materials. These polymers are known for their durability and resistance to heat, chemicals, and deformation. Because of these properties, thermosetting polymers are often used in applications that require strong, long-lasting materials, such as in the automotive and aerospace industries.