Disclosed are articles of manufacture comprising ionomeric copolymers blended with organic acids or salts thereof that have a unique combination of high stiffness and resilience. Articles of manufacture according the invention include, without limitation, footwear structural components (e.g., heel counters, toe puffs, and soles), golf club components, and industrial applications (e.g., materials such as caulking materials, sealants, modifiers for cement and asphalt, coatings, packaging films, molded parts, and resilient foams for sporting goods).