Chlorosulfonated Polythene Rubber (CSM)

CSM, also known as Chlorosulfonated Polyethene rubber, is a high-performance synthetic elastomer made by reacting polyethene with chlorine and sulfur dioxide. This process creates a chemically robust polymer with exceptional resistance to weathering, ozone, UV light, and a wide range of industrial chemicals. In terms of structure and performance, it is similar to chloroprene but offers superior resistance to ageing, UV degradation, and chemical exposure.

In rubber moulding, CSM is valued for its ability to retain strength, flexibility, and colour stability even after long-term exposure to harsh outdoor or corrosive environments. The material also offers inherent flame resistance, good abrasion performance, and reliable ageing characteristics.

CSM rubber (Chlorosulfonated Polyethene) is a durable synthetic rubber used in a wide range of applications that demand exceptional resistance to weathering, UV light, ozone, and chemical exposure. Its stability and durability make it particularly valuable in outdoor environments and industrial settings where long service life is essential. One of the most common uses for CSM is in cable and wire sheathing, where its flame resistance and ability to withstand sunlight and oxidation make it ideal for marine wiring, outdoor electrical systems, and industrial cable assemblies.

CSM is also widely used for hose covers and tubing. Its resistance to abrasion, heat, and aggressive chemicals makes it suitable for chemical hoses, automotive fuel and air lines, and industrial hose systems that operate in harsh conditions. In the automotive sector, CSM is moulded into components such as bellows, boots, static seals, and exterior trim parts, offering a reliable combination of mechanical strength, heat resistance, and environmental durability.

Sealing products such as gaskets, O-rings, and industrial seals are another important area where CSM can perform well, particularly in static applications. It offers strong resistance to oxidising atmospheres, chemical splash, and long-term outdoor exposure. However, CSM is not recommended for dynamic sealing applications because it typically exhibits poor compression set, meaning it may not recover its shape reliably under repeated movement or continuous deformation.

Chlorosulfonated Polyethene is also used in chemical-processing and industrial plants, where it can be moulded into diaphragms, protective covers, tank linings, and other components that come into contact with corrosive or oxidising substances. In the construction sector, CSM can be found in roofing membranes, flashing, and other protective mouldings designed for long-term outdoor exposure. Even sporting goods, inflatable structures, and safety equipment make use of CSM’s combination of strength, flexibility, and colour stability.

From material selection to the moulding process itself, Kea-Flex is here to advise you at every stage of your project. As rubber moulding experts with years of experience, we can help you determine whether CSM, or an alternative elastomer, is the right fit for your specific project.

CSM rubber offers a unique balance of properties that sets it apart from common elastomers such as EPDM and NBR. Compared with EPDM, CSM provides noticeably better resistance to chemicals, oils, and fuels, while still delivering excellent performance against ozone, UV light, and weathering. EPDM is often more cost-effective for general outdoor sealing, but CSM is preferred in harsher environments where chemical splash, oxidising atmospheres, or long-term sunlight exposure are concerns.

When compared with NBR (Nitrile rubber), CSM does not match NBR’s strong oil and fuel resistance, but it significantly outperforms NBR in outdoor durability, heat ageing, flame resistance, and resistance to oxidation and ozone. This makes CSM more suitable for external automotive parts, protective covers, and components that must withstand prolonged exposure to the elements.

Overall, CSM occupies a useful middle ground, offering better environmental and chemical resistance than EPDM, while providing far greater weathering and ageing stability than NBR. This combination makes CSM a highly reliable choice for moulded products that need consistent, long-term performance in demanding service conditions.

Chlorosulfonated Polyethylene (CSM) is generally considered a mid- to premium-priced elastomer, especially when compared with more common materials like EPDM or NBR. Its higher cost is largely due to the more complex manufacturing process, which involves chlorinating and sulfonating polyethene. This makes CSM more expensive per kilogram than many general-purpose rubbers.

However, the initial material cost doesn’t tell the whole story. CSM offers significantly better resistance to UV, ozone, weathering, and chemical attack than EPDM or NBR, which means components made from CSM typically last much longer in harsh environments. For applications exposed to sunlight, chlorine, oxidising atmospheres, or outdoor weather conditions, CSM often proves more cost-effective over the lifetime of the product because it requires fewer replacements and provides more reliable long-term performance.

CSM is a versatile elastomer that performs well across all major rubber moulding processes, including compression, transfer, and injection moulding. Its good flow characteristics, stable cure behaviour, and resistance to porosity make it suitable for both simple and complex geometries. Compression moulding is commonly used for medium- to large-sized parts where durability and consistency are key, and CSM compounds respond well to the controlled pressure and heat used in this method. Transfer moulding is often chosen for components requiring more intricate shapes or metal bonding, as CSM accepts bonding agents effectively and offers reliable adhesion to metal inserts.

Injection moulding is also a strong option for CSM, particularly for high-volume production or detailed components that benefit from precise cavity filling and tight dimensional control. Modern CSM formulations can be optimised for faster cure rates, allowing efficient cycle times even in injection systems. Across all processes, the material’s excellent heat and ageing resistance ensure that moulded parts maintain their stability during both curing and long-term service.

Yes. One of the notable advantages of CSM rubber is its inherent flame-retardant behaviour. Because the polymer contains chemically bound chlorine, CSM naturally resists ignition and can self-extinguish once the flame source is removed. This gives it superior fire performance compared with many non-halogenated elastomers, which often require additional flame-retardant additives to achieve similar results. In practical terms, CSM mouldings are less likely to support combustion, and they generate relatively low levels of smoke and toxic by-products when exposed to heat.

Many CSM formulations are specifically designed to meet industry fire-safety standards, making the material a popular choice for electrical insulation, cable sheathing, transportation components, and industrial equipment used in environments where flame resistance is essential. Although exact performance depends on the compound, CSM generally offers a higher baseline of fire resistance than rubbers such as EPDM, NBR, or even standard Neoprene. Overall, CSM’s inherent flame-retardant properties make it a dependable option for moulded products requiring enhanced fire safety and long-term durability.