Material Comparison8 min read
Gasket Material Selection Guide
A rubber gasket fails for one of two reasons: the compound was wrong for the fluid, or the compound was wrong for the temperature. Everything else — hardness, thickness, flange standard, bolt load — is downstream of those two answers. This guide sets them in order, then shows how to write the result as a specification a manufacturer can quote against.
Published 2 September 2026 · Updated
How do you choose a rubber gasket material?
Step 1: Name the fluid, not the industry
“It is for a pump” is not a specification. “It sees hydraulic oil at 80 °C” is. Fluid compatibility eliminates more compounds than any other criterion, and it eliminates them absolutely — a gasket in the wrong elastomer does not last a shorter time, it swells, softens and extrudes out of the joint.
Two swaps account for most of the failures we are asked to investigate. EPDM in mineral oil: EPDM is excellent in water, steam, brake fluid and dilute chemicals, and it swells badly in petroleum oils. NBR in steam or hot water: nitrile is the default for oils and fuels, and it hardens and cracks in steam. The two compounds are near-opposites, they cost about the same, and they look identical.
Write the fluid down before anything else — including its concentration, its temperature, and whether the gasket is immersed or only splashed. A gasket wetted on one face is a different specification from one sitting in the fluid.
Step 2: Give the continuous temperature, and the cold end too
Most enquiries give a peak temperature. Peak is the wrong number. An elastomer tolerates a brief excursion well above the figure it can hold indefinitely, and specifying against the peak buys a compound several times more expensive than the duty needs.
The cold end is the one more often missed. A gasket that is perfectly specified at +150 °C can be the wrong part at −30 °C, because an elastomer below its low-temperature limit is not a seal — it is a rigid ring that has stopped recovering. Standard fluoroelastomer grades stop at about −20 °C, which is why a compound chosen for heat can fail on a cold morning.
Give both ends, and say which is continuous and which is an excursion. Two numbers and one word decide the compound.
Step 3: Turn the two answers into an ASTM D2000 line callout
ASTM D2000 is how a rubber material is specified on a drawing, and its structure is the two questions above in the order this guide asks them. The Type letter is the temperature answer. The Class letter is the fluid answer. A callout reads as a single string, and every character in it is a requirement a supplier must meet.
Take M2BG714. M means the results are in SI units. 2 is the grade. B is the Type — tested after 70 hours of heat ageing at 100 °C. G is the Class — a maximum of 40 % volume swell after 70 hours in IRM 903 oil. 7 is 70 ± 5 Shore A. 14 is a minimum tensile strength of 14 MPa. That string describes a mid-grade nitrile, and it says so without naming a polymer — which is the point. D2000 specifies performance, so any compound that passes is acceptable.
| Type | Heat ageing, 70 h at | Type | Heat ageing, 70 h at |
|---|---|---|---|
| A | 70 °C | F | 200 °C |
| B | 100 °C | G | 225 °C |
| C | 125 °C | H | 250 °C |
| D | 150 °C | J | 275 °C |
| E | 175 °C | K | 300 °C |
| Class | Max volume swell, IRM 903 | Class | Max volume swell, IRM 903 |
|---|---|---|---|
| A | No requirement | F | 60 % |
| B | 140 % | G | 40 % |
| C | 120 % | H | 30 % |
| D | 100 % | J | 20 % |
| E | 80 % | K | 10 % |
The letter pair is a shorthand for a polymer family. AA covers natural rubber, SBR, butyl and polybutadiene. CA is ethylene propylene. BE is neoprene. BF, BG and BK are nitriles of increasing oil resistance. FE and GE are silicones. HK is fluorocarbon. KK is perfluoroelastomer. Reading the pair tells you the family before you read anything else.
If you have no callout, send the fluid, both temperatures and the hardness you want, and we will write one with you. A drawing that carries a D2000 line is quotable by any competent manufacturer in the world — including the next one, if we are not the right supplier.
The material matrix: eight compounds, ranked by what they seal
| Compound | Temperature | Hardness | Right for | Wrong for |
|---|---|---|---|---|
| NBR (nitrile) | −30 to +120 °C | 40–90 Shore A | Mineral oils, fuels, greases, hydraulic fluid. The default industrial gasket | Steam, hot water, ozone and UV exposure |
| EPDM | −40 to +140 °C | 40–90 Shore A | Water, steam, brake fluid, dilute acids and alkalis, outdoor exposure | Mineral oil, fuel, grease — it swells and extrudes |
| FKM (Viton®) | −20 to +250 °C | 60–90 Shore A | Hot oil, fuels, solvents, aggressive chemicals | Steam, brake fluid, ketones, amines — and cold below −20 °C |
| Silicone | −60 to +220 °C | 30–80 Shore A | Wide temperature range, dry heat, static seals with low load | Mineral oil, steam, abrasion, anything that tears |
| Neoprene (CR) | −40 to +120 °C | 40–90 Shore A | Refrigerants, mild oils, weathering — a good general-purpose middle | Strong acids, aromatic solvents, hot oil |
| AEM | −40 to +175 °C | 50–80 Shore A | Hot oil above nitrile’s ceiling and below fluoroelastomer’s price. Continuous to about +160 °C | Aggressive solvents; and it is absent from most suppliers’ menus |
| SBR | −30 to +100 °C | 40–90 Shore A | Water and air, dry indoor duty, cost-driven volume | Any oil, any fuel, ozone and UV |
| Natural rubber | −20 to +90 °C | 30–80 Shore A | Abrasive slurries, water, high resilience and tear strength | Oil, heat, sunlight |
The matrix does not name a winner because there is not one. Read the “wrong for” column first: on most enquiries it eliminates six of the eight in a few seconds, and the choice between the two that survive is usually about cost, not performance.
Step 4: Which flange standard applies — and the one that does not
A gasket for a pipe flange is drawn to a dimensional standard, and for rubber there are three that matter.
ASME B16.21 — nonmetallic flat gaskets for pipe flanges. This is the standard for rubber. It covers materials, dimensions, tolerances and marking, and its gaskets are dimensionally suited to flanges under ASME B16.5, ASME B16.47, API Specification 6A and ISO 10423.
EN 1514-1 — non-metallic flat gaskets for flanges designated by PN rating, the European equivalent for the same job.
AWWA C111 / A21.11 — rubber-gasket joints for ductile-iron pipe and fittings, the water-industry standard.
The standard that does not apply is ASME B16.20. B16.20 covers metallic gaskets — ring-joint, spiral-wound and metal-jacketed. It is cited for rubber often enough that it has become a common drawing error, and a gasket ordered against it will come back to a dimension that was never meant for an elastomer. If a rubber gasket drawing says B16.20, it is the wrong standard, and the number to check against is B16.21.
Step 5: Thickness, hardness and how hard to do the bolts up
Thinner is usually better. A gasket seals by filling the imperfections in two faces, and once it is thick enough to do that, extra thickness only adds material that can creep, extrude and relax. Thickness should be set by how flat and how parallel the faces are — a machined face needs very little; a warped cast flange needs more.
Hardness follows the same logic. Softer rubber conforms to a poor surface at low load; harder rubber resists extrusion at high pressure. Hardness is not a compatibility property and it is not a quality ranking — 70 Shore A is not “better” than 50, it is stiffer, and on a thin flange with light bolts it is worse.
Where the gap is large or uneven, the answer is not a thicker solid gasket but a closed-cell sponge one, which fills an irregular gap at a fraction of the closing force. Sponge is specified on density and compression force deflection rather than on Shore A.
For bolted flange design, ASME Boiler and Pressure Vessel Code, Section VIII Division 1, Mandatory Appendix 2 tabulates the gasket factor m and the minimum design seating stress y in Table 2-5.1, with effective seating widths in Table 2-5.2. m is the multiple of operating pressure the joint must hold; y is the stress needed to make the gasket flow into the flange face. Rubber sits at the low end of that table, which is exactly why the commonest field failure on a rubber gasket is over-tightening. Take the values from the table or from your gasket supplier — not from a rule of thumb.
What gets tested — and which tests we run ourselves
A specification is only as good as what is measured against it. We test tensile strength and elongation to ASTM D412, and compression set to ASTM D395 Method B, in our own lab in Nashik, and both results ship with every consignment alongside a dimensional report and a certificate of conformance.
Other properties in a D2000 callout — volume swell in IRM 903, heat ageing at the Type temperature, low-temperature performance — are arranged through an external laboratory where a customer requires them. We would rather say so than imply a capability we would subcontract anyway.
One distinction is worth knowing. ASTM D2000 classifies rubber. ASTM F104 classifies nonmetallic gasket materials — the compressed fibre, cork and cellulose sheet products bound with binders and impregnants. They are different families of product and different specification systems, and a callout written in the wrong one will not describe the part you want. A moulded or cut rubber gasket is a D2000 part.
We hold ISO 9001:2015 — certificate 09111526A, Integral Certification Ltd, valid to 21 February 2027, scope: rubber moulded components. That is a quality-management certification, not a product approval. We hold no potable-water, food-contact or pharmaceutical approval, so where a gasket touches drinking water — including the AWWA C111 duty above — that approval has to come from elsewhere. We are upgrading to IATF 16949, targeted by the end of 2026.
Five mistakes behind most gasket failures
Specifying the peak temperature
Peak buys a compound several times more expensive than the duty needs. Give the continuous temperature and note the excursion separately.
EPDM on an oil line, nitrile on a steam line
The two commonest swaps in the industry. Similar price, similar appearance, opposite chemistry — and each fails completely in the other’s duty.
Citing ASME B16.20 for a rubber gasket
B16.20 is the metallic gasket standard. Rubber is B16.21. The wrong reference produces the wrong dimension.
Over-tightening the bolts
Rubber needs a fraction of the seating stress a fibre gasket needs. Past that point the gasket extrudes out of the joint and the leak appears at the moment of assembly.
Treating “Viton” as a specification
It is a trademark covering many fluoroelastomer grades with different low-temperature limits and different cure systems. Specify FKM with a D2000 callout, not a brand name.
Frequently asked questions
Which rubber is best for hot oil?
Nitrile to about +120 °C, which covers most duties. Above that, AEM is continuous to about +160 °C and costs far less than a fluoroelastomer. FKM handles up to +250 °C and is the answer where temperature or chemistry genuinely demand it, at several times the price.
Can I use EPDM with oil?
No. EPDM swells badly in mineral oils, fuels and greases — it softens, grows and extrudes out of the joint. Use nitrile instead. EPDM is excellent in water, steam, brake fluid and dilute chemicals, and it is the right answer for all of those.
How thick should a rubber gasket be?
As thin as the flange faces allow. A gasket only has to fill the imperfections in the two faces; beyond that, extra thickness adds material that creeps and relaxes. Machined faces need very little. Where the gap is large or uneven, use closed-cell sponge rather than thicker solid rubber.
Do you supply gaskets to ASME B16.21 dimensions?
Yes — cut or moulded to your drawing, in any compound we mix. ASME B16.21 is the nonmetallic flat gasket standard; B16.20 covers metallic gaskets and does not apply to rubber. If your drawing cites B16.20 for a rubber gasket, tell us and we will check the dimension with you.
What is your minimum order quantity for gaskets?
We supply in bulk. The minimum run is 10,000 pieces per part number, per compound — a gasket in two compounds is two part numbers. Prototype and first-article lots sit outside the minimum. We respond to technical enquiries within 48 hours.
Send the fluid, both temperatures and the flange drawing, and we will come back with a compound recommendation and a D2000 callout you can put on the drawing — whether or not you buy the gaskets from us. We respond within 48 hours.