Nitrile butadiene rubber (NBR) is a butadiene-acrylonitrile copolymer whose five commercial grades are defined by acrylonitrile (ACN) content: 18-24%, 25-30%, 31-35%, 36-41%, and 42-46%, with higher ACN% yielding better oil resistance and lower-temperature flexibility losses [S6].
The same ACN-driven trade-off governs hardness, swelling, and service temperature, which is why spec sheets list ACN% alongside Shore A and temperature limits rather than picking a single "NBR" value for all fluids [S1][S2].
ACN Content Bands and the Oil-vs-Cold Trade-off
NBR grade selection is essentially an ACN-percentage decision: the 18-24% low-ACN band stays flexible down to roughly -40 °C but swells in aromatic hydrocarbons, while the 42-46% high-ACN band resists petroleum oils aggressively but loses low-temperature flexibility and only rates to about -20 °C [S6]. For seal buyers the practical reading is that oil-resistance ratings and TR-10 (or brittle-point) data move in opposite directions as ACN% rises [S1][S2].
Standard Shore A hardness for general-purpose NBR compounds sits in the 70-90 range; a steel-cored wiper such as the ARTIC R09 ships at 90 Shore A over a -30 to 100 °C window with bore diameters from 20 to 120 mm, showing how ACN and filler loading jointly pin the usable envelope [S1]. Hydraulic O-rings and couplings from Parker, WEH, and Trelleborg list NBR or HNBR seals across 16-345 bar working pressure, again bounded by compound selection rather than fitting geometry [S3].
Modified NBR Sub-Families: HNBR, XNBR, NBR/PVC
Three modified NBRs address the limits of standard grades. Hydrogenated NBR (HNBR) saturates the butadiene backbone, pushing continuous service temperature to roughly 150 °C in oil and adding ozone and sour-gas resistance, which is why Trelleborg, Parker, and CEJN offer HNBR seals for high-pressure hydraulic and CNG fuel systems [S3]. Carboxylated NBR (XNBR) adds carboxylic groups, lifting tensile and tear strength for dynamic rod seals and wipers that see abrasive particles [S1]. NBR/PVC blends (commonly 70/30) upgrade ozone, flame, and abrasion performance for conveyor belts, cable jackets, and sheet gasketing [S2].
The trade-off matrix is concrete: HNBR costs 2-4x standard NBR and is harder to process, XNBR trades compression-set for abrasion, and NBR/PVC loses elasticity at low temperature, so a -40 °C refrigeration line should still go to a low-ACN NBR rather than any modified grade [S2][S3]. Where stability under transformer oil matters, the Trelleborg BF31 NBR sheet at 1,250-1,350 kg/m³ and -40 to 130 °C is a typical reference point for unmodified NBR [S2].
Hardness, Density, and Physical Property Anchors
For NBR sheet goods the published envelope is 1 mm to 50 mm thickness, 1,200-1,550 kg/m³ density, and Shore A roughly 50-80, with Trelleborg's NBR sheeting family running 1 mm-20 mm (general) and 1 mm-50 mm (roll) for cut gaskets [S2]. The LINAGARD® NBR grade is 3-30 mm thick and rated -20 to 110 °C, used where oil resistance is needed with better abrasion than plain natural rubber sheet [S2].
For finished seals the most common Shore A is 70 or 90, with 90A standard for wipers and rod seals exposed to contamination, and 70A typical for O-rings and gaskets where conformance to flange surfaces matters more than extrusion resistance [S1][S3]. The Trelleborg ESDR0 antistatic double-layer sheet pairs a conductive NBR/NR bottom with a static-dissipating NBR top, illustrating how NBR is also specified for electrical-resistance-controlled flooring and ESD workbenches rather than only fluid sealing [S2].
Standards Governing NBR Compound Selection
SAE AMS3200F-1983 covers NBR sheet, strip, tubing, extrusions, and molded shapes rated 55-65 Shore A for petroleum-base hydraulic-fluid resistance, and is the historical anchor for hydraulic seal stock [S5]. SAE AMS3201J-1990 defines a 35-45 Shore A NBR for dry-heat service, giving buyers a lower-hardness option where conformability matters more than extrusion resistance [S7]. These AMS grades overlap with ASTM D2000 line-call-out notation, which is how most procurement specs reference NBR by ACN%, hardness, tensile, elongation, and fluid-swelling limits in a single string.
For end-use assemblies, ISO 3601 governs O-ring housings, and EN 14420-2 covers shank dimensions for NBR-sealed hose couplings, both of which assume an NBR or HNBR element has already been qualified under the AMS or D2000 call-out [S3]. As one DirectIndustry manufacturer note states, "the wiper material is a nitrile rubber NBR 90 Shore A with steel core AISI 1010. Compound reference: NG," showing how compound references (e.g. NG, NBR 70) and the AISI core material travel together on a drawing, not separately [S1].
Industrial Use Cases by NBR Type
Low-ACN NBR (18-30%) is standard for automotive fuel-system O-rings, refrigerant seals, and pneumatic fittings that must pass -30 to -40 °C cold-flex tests, and Parker Legris's 0133 series self-fastening NBR hose (0.125-0.75 in, 0-16 bar) is representative [S3]. Mid-ACN NBR (31-35%) covers general hydraulic cylinders, transformer-oil gaskets (Trelleborg BF31), and hydraulic couplings up to 3,000 psi (Parker 6100 series, 0.75-1.5 in) where balanced swell and cold performance are needed [S2][S3].
High-ACN NBR (36-46%) is reserved for crude-oil, gasoline, and aromatic-fluid service, while HNBR displaces standard NBR above 120 °C and in sour-gas or R-134a refrigerant exposure (Parker TW hydraulic fittings, 345 bar; WEH TW03/TW04 test connectors) [S3]. NBR/PVC blends dominate printing rolls, conveyor skirts, and oil-resistant cable jackets, and NBR/NR ESD laminates cover antistatic flooring where a single 2 mm layer will not dissipate charge safely [S2]. For dynamic rod sealing, the comparison in FKM sealing grades and selection criteria shows where FKM, rather than HNBR, is the correct upgrade for hot oils and aggressive chemicals.
Selection Criteria and Comparison Table
On four decision criteria, the major NBR families line up as follows. (1) Oil resistance rises with ACN% and is best in HNBR, worst in low-ACN NBR. (2) Low-temperature flexibility is best in 18-24% ACN NBR, worst in HNBR and NBR/PVC. (3) Heat ageing tops out at roughly 150 °C in HNBR versus 100-120 °C in standard NBR, and roughly 100 °C in NBR/PVC. (4) Cost per kilogram rises from standard NBR (baseline) through NBR/PVC (~1.2-1.5x) to HNBR (~2-4x), with XNBR priced for abrasion-critical parts only. For fluid-handling O-rings and wipers, silicone rubber grades are the right cross-check when the service fluid is dry heat or food-grade, not petroleum. [S2]
For the buyer, the gate questions are: what is the continuous service temperature, what is the lowest temperature the seal must pass (TR-10 or low-temperature flex), what is the ACN% called out on the compound datasheet, and which standard reference (SAE AMS3200, AMS3201, ASTM D2000 line call-out) matches the application [S5][S7]. A nitrile element specified only as "NBR" without Shore A, ACN%, and a standard is not yet a compound - it is a marketing line.
Limits, Failure Modes, and Recyclability
Standard NBR fails in three predictable modes: extrusion at high pressure when hardness is below 80A, volume swell in aromatic or polar solvents, and hardening/cracking above 100 °C in air or above 120 °C in oil. These are the failure modes that drive HNBR, XNBR, and NBR/PVC substitution in the first place [S1][S3]. Devulcanization research published in 2023-2024 demonstrated that recycled waste NBR can be reprocessed with retained mechanical properties, though the work is still at lab scale (article ranked in the 1st percentile of tracked articles of similar age) [S4].
For buyers running NBR above 100 °C continuously, in ozone-rich outdoor exposure, or in aromatic solvents, the safer default is to step up the family rather than over-spec a thicker standard NBR cross-section; the seal that survives on ACN% rarely survives on cross-section alone [S1][S2].
Trackable signals to watch: any revision of SAE AMS3200/3201 series, expansion of HNBR supply past the current 2-4x premium band, and uptake of devulcanized recycled NBR in commercial sheet and O-ring lines. The DirectIndustry manufacturer index for NBR sheet (7 companies, 10 products) and NBR fittings (31 companies, 157 products) is the leading indicator of which grades are actively being quoted in 2026 [S2][S3].
For component-level specifications, see nitrile rubber, epdm rubber, and industrial rubber.