Short answer: choose silicone for a wide temperature range or prolonged outdoor exposure; choose NBR (or FKM) for oil contact (lubricants, fuel, hydraulic fluid); consider TPU where abrasion resistance, low cost and mild temperatures matter most. Getting the material wrong rarely means "slightly worse" — it usually means a leak or early cracking, so define the operating conditions before discussing price.
Two concepts need untangling first. One: "rubber" is not a single material — NBR, EPDM and FKM behave very differently, so "just use rubber" is not a specification. Two: silicone has poor oil resistance. It excels at temperature and weathering, but swells and loses strength on contact with non-polar oils. This is the single most common way seal selection goes wrong.
| Dimension | Silicone (VMQ) | NBR | EPDM | TPU |
|---|---|---|---|---|
| Temperature range | About −60 °C to +230 °C — the widest | About −30 °C to +120 °C | About −50 °C to +150 °C | About −30 °C to +90 °C |
| Oil resistance | Poor; swells markedly in non-polar oils | Excellent — the standard oil-resistant rubber | Poor, similar to silicone | Good |
| Weathering and ozone | Excellent | Moderate; usually needs protective additives | Excellent — a top outdoor choice | Good, though long-term hydrolysis needs assessment |
| Compression set | Excellent; good recovery and lasting seal | Good | Good | Moderate; creeps under prolonged compression |
| Hardness range | About 10–80 Shore A | About 40–90 Shore A | About 40–90 Shore A | About 70 Shore A to 55 Shore D |
| Abrasion resistance | Moderate | Good | Good | Excellent — its standout strength |
| Food-contact suitability | Food-contact grades widely available | Some grades qualify; confirm individually | Some grades qualify; confirm individually | Some grades qualify; confirm individually |
| Colour and clarity | High transparency and vivid colours possible | Usually black or dark shades | Usually black | Transparent and multi-colour possible |
| Relative cost | Medium-high | Low | Low to medium | Low to medium |
| Typical sealing use | Wide-temperature duty, outdoor equipment, food and medical, transparent parts | Hydraulics and pneumatics, fuel systems, gearboxes, oil seals | Outdoor construction, water systems, automotive door and sunroof seals | Abrasion-resistant lips, wipers, seals needing high strength |
Four Typical Scenarios
The seal contacts lubricant or fuel — which one?
Choose NBR; if temperatures are also high (above 120 °C), consider FKM. This is the one scenario where silicone must not be used — it swells substantially in non-polar oils, with volume change reaching the mid-teens percent or more, which collapses the sealing pressure and shows up as a leak. If your drawing specifies silicone but the duty is an oil circuit, revisit the material.
A wide temperature span (−40 °C to 200 °C)?
Choose silicone. Its temperature window is the widest among common elastomers (typically −60 °C to +230 °C): it stays flexible when cold and does not harden when hot, making it the default for wide-range duty. NBR stiffens noticeably below −30 °C, and EPDM caps out near 150 °C, so neither spans this range. Note that wide-range duty usually also demands low compression set, another area where silicone performs well.
Permanently outdoors — sun, rain and ozone?
Both silicone and EPDM work well; both resist weathering and ozone strongly. The trade-off is temperature and appearance: choose silicone where a wider temperature span or coloured/transparent appearance is needed (visible trim seals, for example); choose EPDM where temperatures are mild, black is acceptable and cost leads (building and automotive door seals). Avoid NBR outdoors — its ozone resistance is only moderate and it tends to crack over prolonged exposure.
Food contact plus abrasion resistance?
Separate the primary from the secondary requirement. If food contact is mandatory, food-grade silicone usually remains the base choice, with abrasion shortfalls addressed through design (thicker sealing lips, lower sliding speed, better surface finish). If abrasion governs service life and the food-contact requirement is looser, evaluate food-contact TPU grades. Few general-purpose grades satisfy both, so document the real operating conditions and confirm with your supplier.
Selection Checklist
- List every contact medium: oil, water, acids, solvents, gases — this alone decides the material
- State the temperature range, separating continuous from brief peak values
- Define the pressure rating and whether low compression set is required
- Confirm static versus dynamic sealing (dynamic demands far more of abrasion and recovery)
- Confirm any food-contact or medical compliance need, and the target market
- Confirm mounting method and compression ratio — the right material still leaks at the wrong compression
- Confirm appearance requirements: transparency, colour or specific surface finish
- Request the material grade with compatibility data for your duty, not just a price
FAQ
Is silicone truly not oil resistant at all?
More precisely, silicone is poor against non-polar oils (mineral oils, fuel, certain lubricants) while performing well against polar media (water, some alcohols, mild acids and bases). So it is wrong to say flatly that silicone fears oil or does not — what matters is which class of medium you contact. Fluorosilicone (FVMQ) covers both oil and heat, but at a much higher cost and normally only when genuinely needed.
Can different seal materials be mixed on one machine?
Yes, and it is common — different locations see different conditions. A hydraulic cylinder might use NBR on the oil circuit and silicone for the external wiper or high-temperature zone. The requirement is to specify the material position by position, not to standardise the whole machine on one compound. List the conditions and material per location on the drawing, so later maintenance does not substitute the wrong material — a frequent cause of leaks.
Correct material but it still leaks — why?
Three common causes, none of them the material. First, the compression ratio is wrong — too little cannot form a seal, too much accelerates permanent set. Second, the groove dimensions and surface finish do not match, so the seal cannot seat stably. Third, damage during installation (scoring, twisting, nicking). Material selection is only step one; groove design and assembly practice decide the outcome just as much. Validate under real conditions during sampling rather than relying on material data sheets alone.
LXYSILICONE manufactures seals in silicone, NBR, EPDM and other materials to your operating conditions, helps assess media compatibility and compression-ratio design, and provides material certificates and test reports on request.