Choosing the right O-ring involves more than just size and material. One of the most critical but often overlooked factors is the material hardness. This indicates how soft or firm a rubber compound is, influencing how well the O-ring seals, resists pressure, and performs in real-world conditions.

For most O-ring applications, Shore A hardness (abbreviated ShA or HA) is the primary scale used. However, understanding how different Shore scales work provides important context for making the best choice.

What Is Shore Hardness?

Shore hardness is a measure of how resistant a material is to indentation, indicating how soft or hard it is on a standardised scale. It is determined using a device called a durometer, which applies a standardised force to a material and measures its resistance to indentation. The result is a numerical value that helps compare the hardness of different materials.

Overview of Shore Hardness Scales

There are several Shore scales, but the most commonly used for polymers and elastomers are:

• Shore A (ShA or HA): Used for soft, flexible materials like rubber, silicone, and other elastomers. This is the standard scale for O-rings. The scale ranges from 0 (very soft) to 100 (very hard). For example, a 70 ShA O-ring offers a balance of flexibility and durability.
• Shore D (ShD or HD): Designed for harder plastics such as nylon, polycarbonate, and rigid thermoplastics. Shore D is not used for standard rubber O-rings, but may be referenced for rigid back-up rings (PTFE) or non-elastomeric sealing components.
• Shore 00: Less common in O-ring applications, Shore 00 is used for very soft gels or foams, like sponge rubber or soft silicone gels.

Which Shore A Hardness Rating is Best for your Application

The Shore A hardness rating of an O-ring has a direct impact on its ability to seal, resist deformation, and withstand pressure. As a guide what rating should you use for different applications.

• Soft O-rings (40–60 ShA): Highly flexible, excellent for low-pressure applications or when sealing against rough or uneven surfaces. However, they may wear more quickly and be prone to extrusion under high pressure.
• Medium O-rings (70 ShA): The most commonly used hardness for O-rings, striking a balance between elasticity and strength. Suitable for both dynamic and static sealing in hydraulics and pneumatics.
• Hard O-rings (80–90 ShA): Best for high-pressure environments. These O-rings are more resistant to extrusion and abrasion but require smooth sealing surfaces and higher installation force.

Reduce Cost and Downtime by Getting your Selection Right

Understanding the Shore Hardness scale, especially Shore A (ShA) for elastomers, is essential for selecting the right O-ring. By matching the material hardness to your application's requirements, you can ensure a more reliable, longer-lasting seal that minimises downtime and maintenance.  To find out more contact our team of experts.

FFKM (Perfluoroelastomer) O-rings are one of the most reliable sealing solutions available, offering unmatched performance in some of the most demanding environments. Combining extreme temperature tolerance, excellent chemical resistance, and mechanical integrity, FFKM has earned its place in industries ranging from aerospace to chemical processing. 

What is FFKM and Why is It So Effective?

FFKM, or Perfluoroelastomer, is a highly fluorinated version of fluoroelastomer that was first developed in the 1960s. Its unique composition gives it the ability to withstand extreme temperatures ranging from -45°C to +330°C, and makes it resistant to over 1,800 chemicals, including hydrocarbons, oils, fuels, and aggressive solvents. This extraordinary versatility is why FFKM is now used extensively across industries that require the highest standards of sealing performance.

Key Benefits of FFKM O-Rings

1. Exceptional Temperature Resistance FFKM O-rings are designed to perform in both extremely high and low-temperature environments. They can withstand temperatures as low as -45°C (-49°F) and as high as 330°C (635°F). This makes them ideal for industries such as aerospace, automotive, and heavy-duty machinery where temperature extremes are common.
2. Unmatched Chemical Resistance One of the standout features of FFKM is its resistance to a wide range of chemicals. With the ability to resist over 1,800 chemicals, solvents, and plasmas, FFKM O-rings ensure reliable performance even in aggressive environments. This resistance makes FFKM ideal for applications in chemical processing, oil and gas, and semiconductor manufacturing.
3. Superior Permeation Resistance FFKM O-rings are highly resistant to gas and liquid permeation, which can lead to seal degradation and failure. Their ability to prevent permeation helps maintain the integrity of the sealing system, extending the lifespan of the equipment and preventing costly downtime or leaks.
4. Weathering and Ozone Resistance FFKM seals are highly resistant to ozone and weathering, making them perfect for outdoor applications. Whether exposed to fluctuating temperatures, humidity, or UV radiation, FFKM O-rings retain their structural integrity and sealing ability. This resistance is essential in industries like automotive and oil and gas, where outdoor exposure is common.
5. Safety and Non-Flammability FFKM O-rings are typically self-extinguishing and exhibit very low flammability in air due to their fully fluorinated polymer structure. This makes them suitable for applications where fire safety and thermal stability are important considerations.
6. Low Outgassing and Extractables In industries like pharmaceuticals, medical device manufacturing, and semiconductor production, outgassing and particle contamination can cause serious problems. FFKM O-rings feature low outgassing properties, ensuring that they don’t release harmful vapors or particles, which is critical for maintaining cleanliness in high-sterility environments.
7. Outstanding Mechanical Properties FFKM O-rings offer excellent compression set resistance and sealing performance, even under mechanical stress. This makes them ideal for heavy-duty machinery, aerospace, and automotive applications, where maintaining a tight seal under pressure is essential.
8. Suitability for Explosive Decompression FFKM is resistant to explosive decompression, a phenomenon that occurs when a material rapidly decompresses under pressure. This resistance prevents rupture, leaks, and seal failures, making FFKM O-rings highly reliable in high-pressure applications.
9. Customisable Shapes and Sizes FFKM O-rings can be easily customized into a variety of shapes and sizes to meet specific application requirements. Whether you need O-rings, gaskets, or custom seals, FFKM's flexibility ensures a perfect fit for your sealing needs.
10. Ultra-Clean Formulas for High-Sterility Environments For applications requiring the highest levels of cleanliness, such as pharmaceuticals and semiconductor manufacturing, FFKM O-rings are available in ultra-clean formulations. Manufactured in cleanroom environments, these seals are free from contaminants, ensuring the integrity of your processes.
11. We can also supply FFKM with approvals such as:
    • 3-A
    • AED/RGD
    • BfR XXI
    • FDA
    • Low Temperature
    • NORSOK M-710-2
    • NORSOK M-710-3
    • Steam Resistance
    • USP Class VI

Applications of FFKM O-Rings in Different Industries

Given the exceptional benefits of FFKM, it's no surprise that this material is used across a wide range of industries. Here are some of the key applications:

• Chemical Processing: FFKM O-rings are ideal for chemical processing applications, including reaction column seals, chemical fluid handling, and heavy-duty cleaning processes. Their chemical resistance makes them perfect for handling aggressive solvents and chemicals.
• Oil and Gas: In the oil and gas industry, FFKM is commonly used for sealing applications in pump and motor stators, packer elements, and critical sealing parts exposed to hydrocarbons and fuels. Its ability to withstand harsh chemicals and extreme pressure makes it a trusted material for this industry.
• Aerospace: Aerospace applications require materials that can handle extreme temperatures, pressure variations, and environmental stress. FFKM is ideal for use in aircraft engines, seals, and piston rings, where performance reliability is paramount.
• Heavy-Duty Machinery: FFKM O-rings are used in heavy-duty machinery where seals are subject to high mechanical stresses. Industries such as manufacturing, construction, and mining benefit from the durability and performance that FFKM seals provide.
• Automotive: FFKM's resistance to high temperatures, ozone, and a wide range of chemicals makes it a perfect fit for automotive applications. It is widely used in fuel systems, injectors, and high-pressure pumps, ensuring long-lasting, reliable performance in automotive environments.

Why Choose FFKM O-Rings from Polymax?

At Polymax, we specialise in providing top-quality FFKM O-rings and sealing solutions for a wide range of industries. Our FFKM O-rings are manufactured to the highest standards to meet the demanding needs of your applications. Whether you are in aerospace, chemical processing, or automotive, we offer the perfect sealing solution to improve efficiency, reduce downtime, and enhance safety.

We can supply FFKM compounds similar to:

The Polymax team can also work closely with designers and engineers to identify a Polymax compound suited to your specific application. We can support your development process with detailed datasheets, helping you confidently specify the correct material for both current requirements and future designs.

Contact Polymax today to find out how FFKM O-rings can enhance your sealing applications. Let us help you choose the right material and design to meet your specific needs, ensuring performance, reliability, and long-term success. Contact our team on: +44 (0) 1420 474 123 or [email protected]