Diundecyl phthalate is primarily used as a plasticizer in the production of flexible polyvinyl chloride (PVC) products. It enhances the flexibility, durability, and workability of PVC, making it suitable for applications such as cables, wires, and flooring materials. Its compatibility with PVC and resistance to extraction make it a reliable choice for long-lasting products. Additionally, it is employed in the manufacturing of adhesives, sealants, and coatings, where it improves performance and stability. Its low volatility and high thermal stability also make it suitable for use in high-temperature environments.