Thermosetting resins are a type of polymer that, once cured, cannot be remolded or reheated. They undergo a chemical change during the curing process, which makes them hard and durable. Common examples include epoxy, phenolic, and polyester resins, often used in applications like adhesives, coatings, and composite materials. These resins are known for their excellent heat resistance and mechanical strength, making them suitable for high-performance applications. Unlike thermoplastics, which can be reshaped with heat, thermosetting resins maintain their shape and properties even under extreme conditions, providing long-lasting performance in various industries.