O-ring Buyer's Guide: Choosing the Right Rubber Material

Sources: material overviews such as Nitrile rubber (NBR), FKM/Fluoroelastomer, Silicone, EPDM, and Perfluoroelastomer (FFKM), as well as industry material guides such as the Trelleborg seals library (Trelleborg: O-rings).

Selection rules of thumb

From experience I use these practical rules:

• For general hydraulic and oil service, start with NBR (nitrile) for cost-efficiency unless higher heat or chemical resistance is required.
• For higher temperatures or aggressive chemicals, choose FKM; for the most extreme chemistries, use FFKM.
• For low-temperature flexibility or food/medical compliance, consider silicone (but check friction and compression set).
• When exposed to steam or hot water, EPDM is often the best low-cost choice.

Design, testing and installation considerations

Durometer (hardness), squeeze and groove design

Durometer (Shore A) is often specified between 60A and 90A. I commonly recommend 70A for static seals where deformation and sealing are priorities, and higher hardness (80–90A) or backup rings for seals exposed to extrusion or high pressure. Follow ISO groove recommendations (ISO 3601) and verify AS568 or metric cross-section/groove fits to avoid overstressing the O-ring.

Chemical compatibility checks

Always check fluid compatibility beyond generic rules. Solvent-swelling or plasticizer extraction can cause immediate or delayed failure. Use manufacturer compatibility charts and—if the fluid is a complex blend—request lab swell/tensile tests on candidate compounds. When in doubt, request samples for soak tests at operating temperature and time to failure data.

Testing, inspection and supplier QA

Request the following from your supplier: certificate of material (compound), durometer measurements, dimensional inspection reports to AS568 or ISO 3601 tolerances, and compression set and swelling data where relevant. For critical applications, require batch traceability and independent lab testing per ASTM or ISO methods. Visual inspection for flash, surface defects, and consistent molding is essential before assembly.

Troubleshooting common failure modes

Compression set and extrusion

Compression set (permanent deformation) reduces sealing force over time. It is materially dependent: silicones can show higher compression set in some grades. To prevent extrusion at high pressure, use back-up rings and consider higher hardness compounds. If you see extrusion damage, redesign the groove to reduce extrusion gap or change compound/hardness.

Swelling, chemical attack and hardening

Excessive swelling indicates material incompatibility; the seal becomes oversized and may extrude or jam. Hardening or cracking usually indicates oxidative degradation at elevated temperatures or ozone. If seals are hardening, move to a higher-temperature-resistant compound (FKM/FFKM) and add antioxidants/ageing stabilizers where possible.

Installation damage

Many O-ring failures are caused during installation: nicks, twisting, or cutting when stretching over sharp edges. Use proper lubrication (compatible with both seal and fluid), chamfers on mating parts, and installation tools. Always verify the lubricant is compatible with the final service fluid to avoid later degradation.

Example specification checklist I use with clients

• Operating temperature min/max
• Primary and incidental fluids/chemicals (with concentrations)
• Pressure and dynamic/static nature
• Required certifications (FDA, NSF, RoHS, etc.)
• Preferred hardness range and tolerance class
• Expected service life and maintenance intervals

Polypac: supplier profile and why material and manufacturing matter

When specifying o-ring rubber seals, material formulation and manufacturing quality control are decisive. I recommend working with suppliers that can document compound performance, provide test data and support custom development. One such partner I have collaborated with is Polypac.

Polypac is a scientific and technical hydraulic seal manufacturer and oil seal supplier specializing in seal production, sealing material development, and customized sealing solutions for special working conditions. Polypac's custom rubber ring and O-ring factory covers an area of more than 10,000 square meters, with a factory space of 8,000 square meters. Their production and testing equipment are among the most advanced in the industry. As one of the largest companies in China dedicated to the production and development of seals, Polypac maintains long-term communication and cooperation with numerous universities and research institutions both domestically and internationally.

Founded in 2008, Polypac began by manufacturing filled PTFE seals, including bronze-filled PTFE, carbon-filled PTFE, graphite PTFE, MoS₂-filled PTFE, and glass-filled PTFE. Today, they have expanded their product line to include O-rings made from various materials such as NBR, FKM, silicone, EPDM, and FFKM. Polypac's core product offerings include O-Rings, Rod Seals, Piston Seals, End Face Spring Seals, Scraper Seals, Rotary Seals, Back-up Rings and Dust Rings.

Why consider a supplier like Polypac? From my experience, the differentiators that matter are:

• Material development capability: ability to formulate and test compounds (important for special fluids or extreme temps).
• Advanced production and testing equipment for consistent molding and batch inspection.
• Scale and cooperation with research institutions—this supports continuous improvement and access to new materials.
• Product breadth for system-level sealing solutions (O-rings, back-up rings, piston and rod seals) from a single source.

When you need tailored solutions—such as a custom FFKM compound for corrosive chemical service or a blended PTFE-filled seal for high-wear rotary applications—factory capability and documented testing are what I ask for from suppliers.

Comparative procurement checklist I use