Surround Material Types of surround material have certain benefits and drawbacks.Foam This is a material with polyester fibers blended in for extra strength and durability. Cloth or Textile This is the name for a variety of cloth fabrics used for speaker construction. Used to replicate the sound of silk tweeters. Rubber Rubber offers excellent flexibility and durability. Butyl Rubber A rubber/butylene compound with excellent flexibility and durability. Santroprene This is a popular new durable plastic material used in many different products apart from speakers. Urethane Urethane is a plastic compound with proven flexibility and weather resistance and is an advance on natural rubber.