IIR
ASTM CIIR, BIIR
IIR is an isobutylene-isoprene copolymer with the lowest gas permeability of the common elastomers; halogenated versions (CIIR, BIIR) add cure sites for faster vulcanisation and better bonding to NR/SBR carcasses.
Reference datasheet — IIR is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the IIR-GP condition
IIR grades and fills
IIR is supplied in 10 conditions, soft to hard. IIR-GP is the default FabDigit quotes; the values on this page are for it.
Compare all 10 grades and fillsHide
| Grade · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness |
|---|---|---|---|---|---|
Closed-cell butyl sponge / foam | Low-density compressible weather and acoustic sealing with very low water/vapour transmission. | 1 | 200 | 15 Shore A | |
Shore A 40 | Soft gaskets, damping pads and low-clamp-force seals. | 8 | 750 | 40 Shore A | |
Electrical insulation grade | Cable insulation, splicing tape and mastics where high resistivity plus moisture barrier are required. | 9 | 550 | 12 Shore D | |
Shore A 50 | General static seals and pharmaceutical stoppers needing needle penetration and reseal. | 10 | 680 | 50 Shore A | |
IIR-GPDefault IIR general purpose | Standard butyl compound for inner tubes, vibration damping, weather seals and waterproof sheet. | 12 | 600 | 60 Shore A | |
Chlorobutyl (≈1.2 % Cl), fast/versatile cure, blendable with NR/SBR | Pick when butyl must be co-vulcanized or bonded to diene rubbers, e.g. tire inner liners and tubeless liners. | 12 | 600 | 60 Shore A | |
Bromobutyl (≈2 % Br), fastest cure, best liner impermeability and… | Choose for tubeless tire inner liners and premium pharmaceutical closures needing fast, low-extractable cure. | 13 | 600 | 60 Shore A | |
phenolic resin vulcanization, heat/steam resistant (curing bladders) | Use for tire curing bladders, steam hose and diaphragms exposed to superheated steam above 150 °C. | 13 | 500 | 60 Shore A | |
Shore A 70 | Default hardness for O-rings and pressure-holding seals in brake fluid or steam service. | 13 | 450 | 22 Shore D | |
Shore A 80 | High-pressure seals, rollers and abrasion/extrusion-resistant parts. | 14 | 330 | 30 Shore D |
Supply forms, finishes and certifications
Ways IIR is supplied — form, process route, surface or paperwork — without a datasheet of their own. The property values above apply.
| Option | What it is | Type |
|---|---|---|
FDA | Food-contact / FDA grade | Certification |
PHARMA | Pharmaceutical / medical grade | Certification |
What is IIR?
IIR is an isobutylene-isoprene copolymer with the lowest gas permeability of the common elastomers; halogenated versions (CIIR, BIIR) add cure sites for faster vulcanisation and better bonding to NR/SBR carcasses. Engineers specify it for air retention, high damping and steam resistance in calendered sheet, extruded profile, moulded closures and sponge, at about 12 MPa tensile strength, 600 % elongation and 125 °C maximum service temperature. It swells in hydrocarbon oils and fuels and cannot be welded, and plain butyl cures slowly compared with halobutyl. EPDM is the usual alternative when weathering matters more than permeability. IIR has a density of 1.12 g/cm³ (0.0405 lb/in³), lighter than 64% of polymer grades. Its glass-transition temperature is -68°C (-90 °F). IIR has a tensile strength of 12 MPa (1.74 ksi), weaker than 76% of polymer grades. Elongation at break is 600% and the elastic modulus is 0.01 GPa (7.25×10⁻⁴ Msi).
What is IIR used for?
- tire inner liners
- pharma vial stoppers
- vibration dampers
- roofing
Advantages
- Ductile — tolerates forming and impact — 600%, better than 93% of polymer grades
- Good UV / weathering resistance — 80/100, better than 86% of polymer grades
- Forms and bends easily — 80/100, better than 75% of polymer grades
Limitations
- High mold shrinkage — 2.5%, worse than 93% of polymer grades
- Low stiffness — 0.01 GPa (7.25×10⁻⁴ Msi), worse than 89% of polymer grades
- Difficult to weld — 5/100, worse than 89% of polymer grades
- Difficult to machine — 30/100, worse than 87% of polymer grades
- Poor heat conductor — 0.13 W/m·K (0.0751 BTU/hr·ft·°F), worse than 82% of polymer grades
IIR properties
Typical room-temperature values for IIR-IIR-GP; bars are the position among polymer grades.
Physical3
IIR has a density of 1.12 g/cm³ (0.0405 lb/in³), lighter than 64% of polymer grades. Its glass-transition temperature is -68°C (-90 °F).
Mechanical7
IIR has a tensile strength of 12 MPa (1.74 ksi), weaker than 76% of polymer grades. Elongation at break is 600% and the elastic modulus is 0.01 GPa (7.25×10⁻⁴ Msi).
Thermal8
IIR is rated for continuous service to 125°C (257 °F). It conducts heat at 0.13 W/m·K (0.0751 BTU/hr·ft·°F), worse than 82% of polymer grades. Thermal expansion is 180 µm/m·K (100 µin/in·°F).
Electrical5
IIR is an electrical insulator with a dielectric strength of 25 kV/mm (635 V/mil) and a resistivity of 1×10¹¹ Ω·m.
Chemical & Environmental3
Corrosion resistance is very good (75/100), worse than 66% of polymer grades. UV resistance is very good.
Sustainability4
Producing a kilogram of IIR takes about 105 MJ of energy and emits 4 kg of CO₂ — more than 54% of polymer grades. Typical recycled content is 5%.
Manufacturability6
IIR's machinability is poor (30/100, worse than 87% of polymer grades); weldability not recommended (5/100); formability very good (80/100).
Common Calculations4
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the polymer family
Yield strength against density for every polymer grade FabDigit runs. IIR is highlighted; hover a dot for its name, or open the interactive family chart.
Working with IIR
Is IIR easy to machine?
Cured butyl is not machined conventionally — use die cutting, water-jet or cryogenic trimming; grinding smears and heats the part.
Can IIR be welded?
Not weldable as a thermoset; join by uncured-to-uncured co-vulcanization, butyl splicing tape/mastic, or cyanoacrylate/chlorinated-surface adhesives after abrasion.
Can IIR be formed, bent or molded?
Mix on mill/Banbury below scorch, then compression, transfer or injection mould at 160–190 °C; halobutyl cures much faster and bonds better to NR/SBR carcasses.
IIR chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| isopreneunsaturation for sulfur cure; often quoted as 0.6–2.2 mol % | 0.5 – 3 | 1.7 |
| chlorineCIIR (chlorobutyl) variant only | 1.1 – 1.3 | 1.2 |
| bromineBIIR (bromobutyl) variant only | 1.8 – 2.1 | 2 |
| carbon blacktypical compound loading 40–60 phr (≈25–35 wt %) | ≈ 30 | 30 |
| processing oil / plasticizerparaffinic oil in the compound | ≈ 8 | 8 |
| zinc oxide / stearic acid / sulfur / acccure system | ≈ 4 | 4 |
| isobutylenepolymer backbone (2-methylpropene) | ≥ 97 (balance) |
What surface finishes work on IIR?
Deflash by cryogenic tumbling; surfaces can be talc- or lacquer-coated, chlorinated or plasma-treated for lower friction and for bonding/printing.
Equivalent designations
Standards and trade names that resolve to IIR in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
How much does IIR cost?
IIR is a standard-cost polymer ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
IIR — frequently asked
What is IIR used for?
IIR is typically used for tire inner liners, pharma vial stoppers, vibration dampers and roofing. In short: lowest gas permeability elastomer; high damping, steam resistant; standard pharma closure rubber.
What is the tensile strength of IIR?
IIR has a typical tensile strength of 12 MPa (1.74 ksi) — weaker than 76% of polymer grades. Strength varies by condition: see the 10 listed tempers.
Is IIR easy to machine?
Not especially — machinability is rated poor (30/100, worse than 87% of polymer grades). Cured butyl is not machined conventionally — use die cutting, water-jet or cryogenic trimming; grinding smears and heats the part.
Can IIR be welded?
Not readily — weldability is rated not recommended (5/100). Not weldable as a thermoset; join by uncured-to-uncured co-vulcanization, butyl splicing tape/mastic, or cyanoacrylate/chlorinated-surface adhesives after abrasion.
What surface finishes work on IIR?
Deflash by cryogenic tumbling; surfaces can be talc- or lacquer-coated, chlorinated or plasma-treated for lower friction and for bonding/printing.
Can IIR be formed, bent or molded?
Mix on mill/Banbury below scorch, then compression, transfer or injection mould at 160–190 °C; halobutyl cures much faster and bonds better to NR/SBR carcasses.
What is the maximum service temperature of IIR?
IIR is rated for continuous use to about 125°C (257 °F), and briefly to 165°C. Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does IIR cost?
IIR is a standard-cost polymer ($$), cheaper than about 71% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- Butyl and Halobutyl Rubber Product Data (Exxon Butyl / Bromobutyl) — ExxonMobil Chemical (2021)
- Engineered Materials Handbook Vol. 2 — Engineering Plastics/Elastomers — ASM International (1988)
- ASTM D2000 — Classification System for Rubber Products in Automotive Applications — ASTM (2020)
- GB/T 8657 (IIR) — SAC (2018)
- ISO 8871 — Elastomeric parts for parenterals — ISO (2020)
- Rubber Technology Handbook (Hofmann) / Vanderbilt Rubber Handbook — Hanser / R.T. Vanderbilt (2010)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.