Quick Answer
Butyl rubber material (IIR, Isobutylene Isoprene Rubber) is a synthetic elastomer known for its exceptionally low gas permeability, excellent weather resistance, ozone resistance, chemical stability, and vibration damping properties. Thanks to these butyl rubber properties, IIR rubber is widely used in tire inner liners, pharmaceutical stoppers, roofing membranes, seals, and protective equipment - making butyl rubber uses span the automotive, medical, construction, and industrial sectors.
What Is Butyl Rubber?
Butyl rubber material, commonly abbreviated IIR (Isobutylene Isoprene Rubber), is a synthetic elastomer produced by copolymerizing isobutylene with a small amount of isoprene.
- Chemical Name: Isobutylene Isoprene Rubber (IIR)
- CAS Number: 9010-85-9
- Isoprene Content: typically 0.5%–3% by mole, with isobutylene making up the remainder
butyl rubber molecular structure
The backbone of IIR rubber is built almost entirely from isobutylene units, which give the polymer its dense, saturated hydrocarbon structure and, in turn, its outstanding impermeability to gases. A small fraction of isoprene is copolymerized into the chain specifically to introduce residual double bonds - these unsaturated sites act as cross-linking points during vulcanization, allowing the rubber to be cured into a stable, elastic network without sacrificing the saturated backbone that gives butyl rubber its signature chemical stability.
Isobutylene (majority monomer)
+
Isoprene (minority monomer, 0.5–3%)
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▼
Cationic Copolymerization
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IIR Chain with Cross-Link Sites
(from residual isoprene double bonds)
This structural balance - a mostly saturated backbone with just enough unsaturation to vulcanize - is the underlying reason nearly all of the butyl rubber properties described below (gas impermeability, ozone resistance, chemical stability) exist simultaneously in the same material.
How Is Butyl Rubber Made?
Butyl rubber is manufactured through cationic polymerization, a process quite different from the free-radical or emulsion polymerization used for many other synthetic rubbers.
Polymerization Process
- Cationic Polymerization: Isobutylene and isoprene are copolymerized using a Lewis acid catalyst (commonly aluminum chloride, AlCl₃).
- Low Temperature: The reaction is typically carried out in methyl chloride as a diluent at very low temperatures (often below −90°C), which is necessary to control the extremely fast, exothermic cationic reaction and achieve the desired molecular weight.
- Catalyst: Aluminum chloride initiates rapid chain growth, with polymerization reportedly completing in well under a second once initiated.
Manufacturing Flow
Isobutylene
│
▼
Isoprene
│
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Cationic Polymerization (AlCl₃ catalyst, methyl chloride diluent, low temperature)
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Coagulation (hot water + food-grade deagglomerating agent, e.g. stearic acid)
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Drying (removal of residual volatiles)
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Butyl Rubber Bale
After polymerization, the rubber particles are treated with hot water and a deagglomerating agent to prevent the particles from sticking together, then dried to remove residual solvent before being pressed into bales for shipment - the standard commercial form of raw IIR rubber.
What Are the Properties of Butyl Rubber?
The properties of butyl rubber are the reason this material occupies a specific, hard-to-replace niche among synthetic elastomers. The table below summarizes the core butyl rubber properties at a glance:
| Property | Rating / Description |
|---|---|
| Gas impermeability | ★★★★★ (best-in-class among common rubbers) |
| Air retention | Excellent |
| Weather resistance | Excellent |
| Ozone resistance | Excellent |
| UV resistance | Excellent |
| Heat resistance | Good |
| Water resistance | Excellent |
| Electrical insulation | Excellent |
| Compression set | Low |
| Abrasion resistance | Moderate |
| Elasticity | Good |
| Chemical resistance | Excellent |
| Steam resistance | Excellent |
| Acid resistance | Excellent |
| Alkali resistance | Excellent |
| Oil resistance | Poor |
| Fuel resistance | Poor |
| Flame resistance | Moderate |
Physical Properties of Butyl Rubber
| Physical Property | Typical Value |
|---|---|
| Density / Specific Gravity | ~0.91–0.93 g/cm³ |
| Hardness (Shore A) | ~40–90 (compound-dependent) |
| Tensile Strength | ~7–20 MPa (compound-dependent) |
| Elongation at Break | ~300–1,000% |
| Operating Temperature | Approx. −40°C to 120°C |
| Glass Transition Temperature (Tg) | Approx. −67°C to −70°C |
| Thermal Conductivity | Low (good insulator) |
| Electrical Resistivity | Very high (excellent dielectric) |
Actual values vary depending on isoprene content, molecular weight, filler loading, and curing system, so these figures should be treated as typical ranges rather than a single fixed specification - always confirm against a specific grade's technical data sheet.
butyl rubber chemical properties
One of the most valuable butyl rubber properties is its highly saturated hydrocarbon backbone, which gives it excellent resistance to a wide range of chemical environments - but leaves it vulnerable to others.
Resistant to:
- Acids (including many concentrated acids)
- Bases / alkalis
- Water and steam
- Alcohols
- Oxidation and ozone
- Oxygen
- Many weak/dilute chemicals
Not Resistant to:
- Mineral oil
- Petroleum-based fluids
- Gasoline
- Hydrocarbon solvents
- Aromatic solvents
This split explains why butyl rubber material dominates in water-, steam-, and gas-barrier applications, but is deliberately avoided in fuel lines, oil seals, or hydrocarbon-solvent-exposed parts, where nitrile (NBR) or fluoroelastomers (FKM) are chosen instead.
Advantages of Butyl Rubber
| Advantage | Why It Matters |
|---|---|
| Extremely low gas permeability | Ideal for tire inner liners and air-retention products |
| Excellent ozone resistance | Long outdoor service life without cracking |
| Excellent weatherability | Reliable performance in outdoor seals and roofing |
| High vibration damping | Effective noise and shock reduction |
| Excellent electrical insulation | Well suited for electrical/cable components |
| Good flexibility | Reliable low-temperature sealing performance |
| Low moisture absorption | Strong performance in waterproofing products |
Disadvantages of Butyl Rubber
- Poor oil resistance
- Poor resistance to hydrocarbons and fuels
- Slow curing/vulcanization rate compared to some other elastomers
- Difficult to bond or adhere compared to more polar rubbers
- Limited high-temperature resistance versus specialty elastomers (e.g., silicone, FKM)
- Generally higher cost than natural rubber
What Is Butyl Rubber Used For?
The breadth of butyl rubber uses reflects how directly its properties map onto real-world performance needs across several industries.
Automotive
- Tire inner liners
- Inner tubes
- Seals and gaskets
- Bushings
Construction
- Roofing membranes
- Expansion joints
- Waterproof sheets
- Sealants
Medical / Pharmaceutical
- Bottle stoppers
- Injection vial closures
- Pharmaceutical packaging components
- Syringe components
Industrial
- Tank linings
- Protective equipment
- Chemical containers
- Shock absorbers
Consumer Products
- Sports balls (bladders)
- Adhesive tape
- Protective gloves
- Rubber sheets
Across every one of these categories, the common thread is the same: wherever a product needs to hold in air, moisture, or gas - or resist ozone, weather, and chemical exposure - IIR rubber is a natural fit.
Butyl Rubber vs. Other Rubber Materials
| Property | Butyl (IIR) | EPDM | Natural Rubber (NR) | NBR | Neoprene (CR) | Silicone | FKM |
|---|---|---|---|---|---|---|---|
| Gas permeability | Lowest (best barrier) | Low | High | Moderate | Moderate | High | Low |
| Oil resistance | Poor | Poor | Poor | Excellent | Good | Poor–Fair | Excellent |
| Heat resistance | Good | Excellent | Fair | Good | Good | Excellent | Excellent |
| Weather resistance | Excellent | Excellent | Fair | Fair | Good | Excellent | Excellent |
| Ozone resistance | Excellent | Excellent | Poor | Poor | Good | Excellent | Excellent |
| Chemical resistance | Excellent (acids/bases) | Good | Fair | Good (oils) | Good | Fair | Excellent |
| Flexibility (low temp) | Good | Good | Excellent | Fair | Fair | Excellent | Fair |
| Cost | Moderate–High | Low–Moderate | Low | Moderate | Moderate | High | Very High |
| Typical Applications | Tire liners, stoppers, roofing | Outdoor seals, roofing, automotive weatherstrip | General-purpose seals, footwear | Fuel/oil seals, hoses | Wetsuits, hoses, belts | Medical, food-grade seals | Aerospace, chemical seals |
This comparison highlights why butyl rubber material is chosen specifically for gas- and air-barrier performance, while EPDM, NBR, neoprene, silicone, and FKM are selected when oil resistance, extreme temperature, or specialty chemical exposure are the priority instead.
Butyl Rubber Temperature Range
| Condition | Typical Range |
|---|---|
| Continuous Service Temperature | Up to ~120°C |
| Intermittent Peak Exposure | Up to ~150°C (short duration) |
| Low-Temperature Flexibility | Down to approximately −40°C |
| Glass Transition Temperature (Tg) | ~−67°C to −70°C |
Butyl rubber retains useful flexibility at low temperatures while maintaining its air/gas barrier performance, though prolonged exposure above its continuous service temperature accelerates hardening and loss of elasticity - a key reason it is rated "good" rather than "excellent" for heat resistance compared to silicone or FKM.
Is Butyl Rubber Waterproof?
Yes. Butyl rubber is considered one of the most effective waterproofing elastomers available, for two closely related reasons:
- Air impermeability: The same dense, saturated molecular structure that blocks gas diffusion also blocks water vapor transmission.
- Water resistance: IIR rubber does not swell significantly or degrade with prolonged water or steam exposure.
This is why butyl rubber material is a preferred choice for roofing membranes, pond liners, and sealants - applications where long-term water exclusion, not just splash resistance, is the requirement.
Is Butyl Rubber Safe?
Butyl rubber's chemical inertness and low reactivity make it broadly compatible with regulated applications, though the specific compliance status always depends on the exact compound and its intended use:
- Food Contact: Certain butyl rubber grades are used in food-contact applications such as chewing gum base and closures, reflecting its low reactivity and low extractable profile.
- Medical/Pharmaceutical: IIR rubber is widely used for pharmaceutical stoppers and closures, with pharmacopeia-grade material commonly referenced against USP, EP, and BP monographs for elastomeric closures.
- Regulatory Frameworks: As with most industrial elastomers, specific formulations may be evaluated for compliance with frameworks such as RoHS (restriction of hazardous substances) and REACH (EU chemical registration), depending on the additives, fillers, and curing systems used in a given compound.
Because compliance depends on the specific formulation (base polymer plus fillers, curing agents, and additives), buyers sourcing butyl rubber material for food, medical, or regulated applications should always request compound-specific compliance documentation rather than assuming it automatically applies to all IIR rubber grades.
Can Butyl Rubber Be Recycled?
Yes, though butyl rubber's crosslinked (vulcanized) network makes recycling more involved than simply remelting a thermoplastic:
- Mechanical Recycling: Cured butyl rubber scrap can be ground into crumb rubber for use as filler in lower-performance rubber compounds, mats, or other non-critical products.
- Devulcanization: Chemical, thermal, or mechanical devulcanization processes attempt to break sulfur crosslinks, partially restoring processability so reclaimed material can be reintroduced into new rubber compounds.
- Pyrolysis: At end of life, butyl rubber scrap can be processed via pyrolysis to recover carbon black and hydrocarbon oil fractions for reuse as fuel or feedstock.
- Sustainability Considerations: As tire and industrial rubber recycling infrastructure expands globally, devulcanization and pyrolysis routes are increasingly relevant to ESG-focused sourcing decisions for IIR rubber-containing products, particularly tire inner liners.
Storage and Handling
| Factor | Recommendation |
|---|---|
| Storage Temperature | Cool, stable temperature; avoid heat sources |
| Humidity | Low humidity, dry storage area |
| Shelf Life | Commonly 24 months from production when stored properly (compound-dependent) |
| Sunlight/UV | Store away from direct sunlight to prevent surface degradation |
| Packaging | Typically supplied in bales, wrapped to prevent dust/talc contamination and sticking |
Proper storage matters most for B2B buyers purchasing raw butyl rubber material in bale form, since improper humidity or heat exposure during storage can affect processability before the material ever reaches the compounding stage.
FAQs
Is butyl rubber natural or synthetic?
Butyl rubber is a fully synthetic elastomer, produced by cationic copolymerization of isobutylene and isoprene - it is not derived from natural rubber latex.
Is butyl rubber waterproof?
Yes. Its dense, saturated molecular structure gives it excellent resistance to both water and water vapor transmission, making it a common choice for roofing and waterproofing applications.
Is butyl rubber flexible?
Yes, IIR rubber remains flexible across a wide temperature range, typically down to around −40°C, while retaining good elasticity at room temperature.
Does butyl rubber crack?
Butyl rubber is highly resistant to ozone- and weather-induced cracking, which is one of its key advantages over rubbers like natural rubber or NBR in outdoor applications.
Is butyl rubber UV resistant?
Yes, butyl rubber offers excellent UV and weather resistance, supporting long service life in outdoor products such as roofing membranes and seals.
Is butyl rubber heat resistant?
Butyl rubber offers good, but not top-tier, heat resistance, with a typical continuous service temperature up to around 120°C - lower than specialty elastomers like silicone or FKM.
Is butyl rubber resistant to gasoline?
No. Butyl rubber has poor resistance to gasoline, petroleum products, and hydrocarbon solvents, and is not recommended for fuel-contact applications.
Why is butyl rubber used in tires?
Because of its exceptionally low gas permeability, butyl rubber material is the standard choice for tire inner liners, where it keeps air from escaping through the tire body and maintains proper inflation pressure over time.
Is butyl rubber better than EPDM?
Neither is universally "better" - butyl rubber has superior gas impermeability, making it the preferred choice for air/gas barrier applications, while EPDM generally offers better heat resistance and is often more cost-effective for general outdoor sealing applications.
What are the disadvantages of butyl rubber?
The main disadvantages of butyl rubber include poor oil and fuel resistance, relatively slow curing, difficulty bonding to other materials, limited high-temperature performance compared to specialty elastomers, and higher cost than natural rubber.