Diisooctyl 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, flooring, and synthetic leather. Additionally, it is employed in the manufacturing of adhesives, sealants, and coatings to improve their performance and longevity. Its compatibility with various polymers also makes it useful in the production of inks and paints, where it aids in achieving desired consistency and finish. In industrial settings, it serves as a lubricant additive to reduce friction and wear in machinery.