Abstract: A method of combining rubbers and plastics when injection molding, and compositions usable in injection molding, are shown and described. Comminuted rubber from waste tires and waste plastics including any of high density polyethylene, polyethylene terephthalate, and polypropylene are combined and heated to melt at least the plastics. In one optional approach, both are melted. Plastics comprise from twenty to eighty percent by weight of the mixture, with rubber accounting for the balance. The mixture may be fortified with bonding, compatibilizing, and strengthening agents. The compositions may be cooled and pelletized for immediate use in injection operations.