O-ring material
Butyl O-Rings
Butyl O-rings are the isobutylene-isoprene rubber (IIR) seal chosen for one property no common elastomer matches: very low permeability to gases. The Parker® O-Ring Handbook rates butyl from -59 C to 121 C, and Conquest supplies butyl O-rings in AS568 and metric sizes as a distributor, quoted in the compound the print names.
- Family
- Butyl (IIR)
- Standard range
- -59 C to 121 C (Parker O-Ring Handbook ORD 5700)
- Durometers
- By compound; the compound sheet states it
- Standards
- ASTM D1418 IIR; ASTM D2000 line callouts on specific compounds
- Product
- O-rings in AS568 and ISO 3601 sizes, quoted in the compound the print names
Ranges are the handbook family figures; the compound datasheet and your application govern the final choice.
Larger and non-standard sizes: an O-ring beyond the molded size lists can be supplied as a spliced and vulcanized O-ring, which the maker joins from cord of the same compound. That page lists, family by family, which makers offer the compound as cord, and what to send for a quote.
What butyl is, and where it is chosen
Butyl is a copolymer of isobutylene and isoprene with a very low permeability rate to gases, which is why it seals vacuum chambers, gas-holding equipment, tank vents and instrument housings that must not breathe. The Parker handbook also lists glycol-based brake fluids, phosphate-ester hydraulic fluids, polar solvents such as ketones, many acids, salt solutions, and ozone and weather among what it resists. The Parker handbook puts the family at -59 C to 121 C, a cold limit most oil-resistant rubbers cannot reach.
Where butyl fails
The Parker handbook lists mineral oil and grease, fuels and chlorinated hydrocarbons as not compatible with butyl, so it is never the seal for a hydraulic system on mineral oil or a fuel line. Where an oil-resistant seal must also hold gas, nitrile or HNBR is the usual compromise; where the gas is the whole job and no oil is present, butyl is the usual fit. The compatibility guide carries the media families.
How to specify
Send the AS568 dash number or the inside diameter and cross-section, the durometer, the medium and the temperature, and say whether the seal holds vacuum or pressure. Name any ASTM D2000 line callout the print carries. The quote names the compound your print or your engineering specifies and sends its datasheet.
Sizes and forms we supply
All 369 AS568 sizes (349 general-purpose dash sizes plus the 20 boss-seal sizes) and the ISO 3601 metric series, in the durometers listed above; O-ring cord for rings spliced and vulcanized by the maker in odd diameters (static service only), where the compound is made as cord. The AS568 chart and the AS568 sizes in millimeters carry the dimensions, and the dash number guide explains the numbering.
Sources: Parker O-Ring Handbook ORD 5700, section 2.2 (read 2026-09-14) (§2.2.5 butyl; §2.2.4 EPDM, up to 150 C); Parker O-Ring Handbook ORD 5700, section 2.2.5 butyl: permeability, chemical resistance and not-compatible lists (read 2026-09-25); AS568 size count, 369 sizes (349 general-purpose plus 20 boss): Parker O-Ring Handbook ORD 5700, section IX size tables (Series 2-XXX and the 3-9XX boss table), read 2026-09-27; ASTM D1418; ASTM D2000 (documents named, not reproduced); Parker O-Ring Handbook ORD 5700, page 2-10 (hardness guidance), read 2026-09-25.
Parker is a trademark of Parker Hannifin Corporation. No affiliation or endorsement is implied.
Frequently asked
What is butyl used for?
Vacuum and gas-holding seals, brake-fluid and phosphate-ester service, and outdoor seals, because it passes very little gas and resists ozone, ketones and many acids.
Can butyl O-rings handle oil?
No. Petroleum oils, greases and fuels swell butyl; nitrile, HNBR or FKM serve those.
What temperature range does butyl have?
The Parker O-Ring Handbook rates butyl from -59 C to 121 C; the compound datasheet governs.
Butyl or EPDM?
Both resist water, brake fluid and weather and both fail in oil. Butyl wins on gas permeability; EPDM runs hotter, to 150 C against butyl's 121 C on the Parker ranges. Name the medium and the temperature; the quote names the compound your print or your engineering specifies.
Which durometer?
The compound sheet states it; for most applications the Parker handbook puts the usual choice at 70 to 80 Shore A (ORD 5700, page 2-10). The durometer guide covers the choice.
Related guides
Orders are handled under Conquest Seal's AS9100D quality management system, whose certificate scope includes distribution.
Send the part number and the quantity for Butyl
The AS568 dash number or the inside diameter and cross-section, the durometer, the quantity, the medium and temperature, and any specification the print names. A Conquest representative replies. Quotes answered within one business day. A person answers (714) 632-9830, Pacific business hours.
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