plasticizer

noun

1. any of a group of substances that are used in plastics or other materials to impart viscosity, flexibility, softness, or other properties to the finished product.
2. an admixture for making mortar or concrete workable with little water.

noun

1. any of a number of substances added to materials in order to modify their physical properties. Their uses include softening and improving the flexibility of plastics and preventing dried paint coatings from becoming too brittle