Impact modifiers are elastomers that are incorporated into a polymer matrix to absorb mechanical energy. The particles of the impact modifier are tied to the matrix by entanglements of the free chain ends with the PVC molecules. Elastomeric modifiers make inherently brittle PVC impact resistant while hardly affecting its other mechanical properties. The use of core-shell impact modifiers yields balanced rigidity, impact strength and hardness. The thermoforming properties of PVC are hardly affected by core-shell particles. The efficiency of the impact modifier depends on the ratio of soft acrylic rubber core to the surrounding shell as well as on the degree of cross-linking of the rubber and the size of the primary particles. Emulsion polymerisation yields a well-defined particle size which ensures a homogenous distribution in the PVC matrix combined with improved processing latitude. Acrylic impact modifiers enhance the weather ability and UV stability of PVC products. Their chemical composition makes DEGALAN® impact modifiers especially suitable for rigid PVC products in outdoor applications.