Polyurethane, categorized as a polymer, is a resilient, flexible and durable manufactured material that can take the place of paint, cotton, rubber, metal or wood in thousands of applications across virtually all fields. It can be hard like fiberglass, squishy upholstery foam that can be protective like varnish, bouncy like rubber, or sticky like glue. In the case of our cones, this material allows for maximum flexibility that produces great sounding speakers lasting a long time.