Polypropylene is any of various thermoplastic resins that are polymers of propylene. They are hard and tough, and are used to make molded articles and fibers. Unlike polybutylene, polypropylene is rated for cold water use only and has withstood the test of time for plumbing applications. For more information about polybutylene visit http://www.polybutylene.com.
[Edited by Polybutylene.com on 17 May 2000]