Diisononyl phthalate, chemical formula C26H42O4, is an organic compound also known as DINP. It is a colorless to pale yellow oily liquid with low volatility and good solubility.

Diisononyl phthalate has excellent plasticizing properties and is mainly used as a plasticizer for plastics. It can increase the softness and ductility of plastic, provide plastic plasticity, and improve the processing performance of plastic. Therefore, it is widely used in the plastic industry, especially in the production of polyvinyl chloride (PVC) products, such as plastic flooring, pipes, wire and cable insulation materials.