Technical Foundation
What Is a Rubber Cord?
Rubber cord is round-profile extruded elastomer sold by the foot or on rolls, used to fabricate custom O-rings, gaskets, and seals in sizes or shapes not available as a stock molded part — the cord is cut to length and the ends bonded together (spliced) to form a closed loop matching the exact groove or bore dimension needed. This makes it a practical solution for large-diameter seals, obsolete equipment repair, or one-off gasket needs where ordering a custom molded O-ring wouldn't be cost-effective.
Elastomer selection follows the same chemical and temperature compatibility logic as molded O-rings: EPDM for water, steam, and weathering resistance; nitrile (Buna-N) for petroleum oils and fuels; silicone for high/low temperature extremes and food-grade applications; and Viton/FKM for aggressive chemicals and high-temperature service. Durometer (hardness) affects how well the cord seals under compression versus how much force is needed to compress it in the groove.
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| Spec | What It Means | Why It Matters |
|---|---|---|
| Diameter | Common sizes from 1/16 in. to 1/2 in. and larger | Must match the groove or gland width the finished seal will sit in |
| Elastomer Type | EPDM, nitrile, silicone, neoprene, Viton/FKM | Determines chemical, temperature, and fluid compatibility |
| Durometer (Hardness) | Typically 40-90 Shore A | Softer durometer seals better at low compression; harder resists extrusion under pressure |
| Temperature Range | Varies by elastomer, roughly -65°F to 500°F across types | Must exceed the actual service temperature range with margin |
| Splicing Method | Cyanoacrylate bonding, vulcanizing splice kits, or heat fusion | Splice strength and finish quality affect the seal's reliability at the joint |
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Applications
Where Rubber Cord Get Used
Rubber cord is specified anywhere a custom-sized or non-stock seal needs to be fabricated rather than ordered as a molded part.
Custom Gasket & Seal Fabrication
Cutting and splicing rubber cord to exact bore or groove dimensions not available in stock O-ring sizes.
Equipment Repair & MRO
Field-fabricated seals for legacy or obsolete equipment where a molded replacement O-ring isn't available.
Large-Diameter Sealing Applications
Splicing cord into large custom-diameter seals more economically than a custom-molded large O-ring.
Food & Beverage Processing
Food-grade silicone cord fabricated into gaskets for process equipment and fittings.
HVAC & Plumbing Equipment Service
Custom-cut EPDM cord used to fabricate gaskets for access panels and equipment covers.
Marine & Outdoor Equipment Sealing
Weather- and UV-resistant EPDM or silicone cord fabricated into hatch and access seals.
FAQ
Rubber Cord Questions, Answered
How do I splice rubber cord into a closed-loop seal?
Cord is cut to the correct length (accounting for stretch and the groove circumference), and the two ends are joined using either a cyanoacrylate adhesive for a quick low-stress bond, or a vulcanizing splice kit that chemically fuses the ends into a near-seamless joint for more demanding sealing applications. Splice kits matched to the specific elastomer type give a stronger, more reliable joint than general-purpose adhesive.
How do I choose the right elastomer for my sealing application?
Match the elastomer to the fluid, gas, or environment the seal will contact: EPDM for water, steam, and weathering; nitrile for petroleum-based oils and fuels; silicone for extreme temperatures and food-grade uses; and Viton/FKM for aggressive chemicals and high heat. Using an incompatible elastomer risks swelling, hardening, or premature seal failure.
What durometer rubber cord should I use for my seal?
Softer durometer (around 40-60 Shore A) seals effectively with less compression force, suiting lower-pressure or hand-tightened applications, while harder durometer (70-90 Shore A) resists extrusion into gaps under higher system pressure but requires more compression force to seal properly.
Can rubber cord replace a standard molded O-ring in every application?
Cord-and-splice seals work well for custom, large, or one-off sizes, but the splice joint is inherently a potential weak point compared to a seamless molded O-ring — for high-pressure, high-cycle, or critical sealing applications where a standard molded size is available, a molded O-ring is generally more reliable.
How do I measure the right length of cord to order for a splice?
Measure the circumference of the groove or bore the seal will sit in, then add a small amount of stretch allowance (the cord should sit slightly compressed, not loose) as specified by the splice kit or elastomer manufacturer's guidance — cutting too short leaves the joint under excess tension, while too long leaves the seal loose in the groove.
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