CSPE (Hypalon) Roofing

CSPE (chlorosulfonated polyethylene), also designated CSM, is a synthetic rubber made by treating polyethylene with chlorine and sulfur dioxide. It was best known under DuPont's trademark Hypalon. For roofing it was made into single-ply membrane sheets for flat roofs.

Use in roofing

CSPE and related CPE membranes were used on low-slope roofs from about 1964. The same material was widely used for geomembranes, pond liners, inflatable boats, cable jackets and automotive hoses.

Discontinuation

On 7 May 2009 DuPont announced it would close its plant in Beaumont, Texas, its only CSM plant, by 30 June 2009, as it was leaving the Hypalon business. At customers' request closure was delayed until 20 April 2010. This ended supply of DuPont Hypalon in the Americas. Most other roofing membrane makers stopped producing CSPE sheets within a few years, and CSPE roofing had almost disappeared by about 2011. CSM rubber is still produced elsewhere, notably by Tosoh in Japan and manufacturers in China, but not generally for roofing.

Alternatives

In geomembrane applications, industry advisers suggested switching to other resins such as flexible polypropylene once Hypalon left the American market. In roofing, owners and designers turned mainly to PVC, KEE, TPO and EPDM.

Existing roofs

Some CSPE roofs remain in service. With new CSPE sheet no longer generally available for roofing, owners reroofing these buildings choose a different membrane system.

Material characteristics

CSM rubber is cured with metal oxides, enabled by the reactive chlorosulfonyl groups introduced during manufacture. Outside roofing it has been prized for long life and resistance to salt water and sunlight, which explains its long use in professional and military inflatable boats.