The plastics additives powder compositions of the present invention are provided as powder particles having impact modifier particles and processing aid particles which are coagulated and dried. When blended in thermoplastic resins, such as PVC, the subject plastics additives powders both increase the impact strength and improve process efficiency and melt strength. The impact and processing properties achieved by the present invention are more efficient than using separate impact modifier and processing aid powders. The method of preparing the powder compositions of the present invention also enable impact modifier particles having rubber weight fractions greater than 88% to be isolated as free-flowing powders.