Rubber Material Engineering Guide
Butyl Rubber (IIR): Properties, Grades, Applications & Selection Guide
Butyl rubber (IIR) is a synthetic elastomer based primarily on isobutylene with a small amount of isoprene. It is valued for very low gas and moisture permeability, strong damping behavior, and resistance to ozone, weathering and aging. IIR is used in airtight and moisture-control components, seals, membranes, bladders, hoses and other custom rubber parts, while chlorobutyl (CIIR) and bromobutyl (BIIR) extend processing and cure options. Final suitability always depends on the exact compound, service media, temperature, geometry and required validation.
Material Fundamentals
What Is Butyl Rubber (IIR)?
Butyl rubber, abbreviated IIR, is a copolymer of isobutylene with a small proportion of isoprene that provides sites for vulcanization. Its densely packed polymer structure gives IIR one of its most important engineering characteristics: very low permeability to gases and moisture compared with many common elastomers.
That barrier behavior is why butyl rubber is strongly associated with tire inner tubes and air-retention systems, but the same material logic also applies to industrial membranes, bladders, seals, hoses, linings, damping components and custom molded parts. The correct material still needs to be selected at compound level because fillers, plasticizers, cure chemistry and part geometry all affect finished performance.
IIR is often considered when
- Low air or gas permeation is a core functional requirement.
- Moisture barrier performance matters.
- Ozone, weathering and aging resistance are important.
- Vibration damping and low rebound are useful.
- Water, selected acids or alkalis are present and the exact medium is compatible.
IIR needs another look when
- Petroleum oils, hydrocarbon fuels or many organic solvents contact the part.
- High resilience or rebound is required.
- Severe abrasion or dynamic tear is the dominant failure mode.
- A pharmaceutical, food, drinking-water or other regulated compound is required.
- Co-vulcanization with other rubber layers makes CIIR or BIIR more appropriate.
Performance Profile
What Are the Key Properties of Butyl Rubber?
IIR is selected mainly for barrier performance, damping and environmental aging resistance. These strengths are most useful when they match the real failure mode rather than being treated as a generic “best rubber” list.
Low Gas Permeability
Low permeability to air and other gases is the defining strength of butyl rubber and a major reason for its use in air-retention and barrier applications.
Moisture Barrier
IIR also provides low moisture transmission, useful for components intended to keep moisture in or out. The actual barrier target should be verified on the finished compound or assembly.
Vibration Damping
Butyl rubber has high damping and relatively low resilience, making it useful where energy absorption is more important than spring-like rebound.
Ozone & Weathering
The highly saturated polymer backbone gives IIR good resistance to ozone, atmospheric aging and outdoor exposure.
Water & Chemical Resistance
IIR can be a strong starting point for water and many selected acid/base environments, but compatibility depends on concentration, temperature and compound formulation.
Low Rebound
Low resilience supports damping but makes IIR a poor choice when a component depends on high rebound or very lively elastic response.
Polymer & Grade Selection
What Is the Difference Between IIR, Chlorobutyl (CIIR) and Bromobutyl (BIIR)?
Regular IIR, chlorobutyl rubber and bromobutyl rubber belong to the butyl family, but they are not interchangeable names. Halogenation modifies cure reactivity and compatibility with other rubber systems, which can materially affect multi-layer products and manufacturing.
| Butyl Family | What Changes | Typical Selection Logic |
|---|---|---|
| Regular IIR | Base isobutylene-isoprene copolymer with low unsaturation | Used when low permeability, damping and aging resistance are central and its cure/adhesion behavior fits the product. |
| CIIR | Chlorinated butyl rubber | Halogenation increases cure reactivity and can improve compatibility/co-vulcanization with other diene rubbers. |
| BIIR | Brominated butyl rubber | Also provides increased cure reactivity and is widely used where fast cure or multi-rubber construction is important. |
| Finished compound | Fillers, curatives, plasticizers, process aids and other ingredients | Controls hardness, processing, compression behavior, color, physical properties and compliance. |
Halobutyl is not automatically “better”
CIIR or BIIR may solve cure, adhesion or multi-layer construction requirements, while regular IIR may remain suitable for a simpler barrier or damping part. Choose by function and manufacturing route.
Do not buy by polymer abbreviation alone
Two IIR compounds can share the same base polymer family yet differ materially in hardness, cure behavior, compression set, extractables, permeability and fluid resistance.
Crosslinking
How Do Cure Systems Change Butyl Rubber Performance?
Butyl compounds can use different vulcanization systems, and regular IIR does not necessarily use the same cure chemistry as CIIR or BIIR. Cure selection affects processing speed, crosslink structure, heat aging, compression behavior, adhesion and final mechanical properties.
| Cure Topic | Engineering Relevance | RFQ / Validation Question |
|---|---|---|
| Regular IIR cure | Low unsaturation requires a cure package designed specifically for the selected IIR compound. | Is the project specifying only final performance, or a particular cure chemistry? |
| Halobutyl cure | CIIR and BIIR offer greater cure reactivity and additional crosslinking options. | Does the part need faster cure, bonding or co-vulcanization with another rubber layer? |
| Resin / specialty systems | Selected IIR applications may use cure systems chosen for specific heat, compression or processing behavior. | Are there aging, extractables or process requirements that restrict the cure system? |
| Cure state | Under-cure or excessive cure can alter compression set, strength, adhesion and dimensional stability. | Which final properties and process controls will define acceptable cure? |
Hardness & Geometry
What Butyl Rubber Hardness Should You Choose?
IIR compounds can be formulated in multiple Shore A hardness grades. The correct value depends on how much the part must deform, seal, damp vibration, support load, resist extrusion and survive assembly.
Lower Hardness
Can improve conformity and reduce compression force, but may increase deformation, handling difficulty or extrusion risk in pressurized sealing geometries.
Medium Hardness
Can balance flexibility, sealing force and dimensional stability for many molded parts. The exact target remains application-specific.
Higher Hardness
Can provide more load support and deformation resistance, but may increase assembly force and reduce conformity to imperfect mating surfaces.
Hardness alone does not define damping, gas permeability, tensile strength or compression set. State both the target Shore A and the permitted tolerance when hardness is a functional requirement.
Thermal Limits
What Temperature Range Can Butyl Rubber Handle?
There is no single temperature range that can be guaranteed for every IIR compound. Regular IIR, halobutyl grades, cure systems and formulations can have different low-temperature flexibility and long-term heat-aging behavior.
Temperature should therefore be specified as an application condition rather than copied from a generic chart. A material that survives a short temperature excursion is not automatically suitable for continuous compression, dynamic flexing or long-term barrier performance at the same temperature.
Minimum Temperature
Define whether the part must remain flexible, seal, move or only survive storage at the minimum temperature.
Continuous Temperature
Long-term heat can change hardness, elongation, compression set, adhesion and barrier performance. Validate the selected compound for the required duration.
Peak Temperature
State the peak value, duration and frequency. Short excursions and continuous service should not be treated as the same requirement.
Temperature + Media
Water, chemicals, gas or hydrocarbon exposure can change aging and swelling behavior. Evaluate media and temperature together.
Fluid Compatibility
Which Chemicals and Fluids Is Butyl Rubber Compatible With?
IIR is often considered for water, moisture, many selected acids and bases, and atmospheric exposure. It is generally a poor starting point for petroleum oils, hydrocarbon fuels and many hydrocarbon or organic solvents. Exact compatibility must be checked against the real fluid, concentration, temperature and exposure time.
| Media Group | General IIR Screening | Engineering Note |
|---|---|---|
| Water & moisture | Strong starting point | Confirm temperature, pressure and any additives or treatment chemicals. |
| Air & many gases | Low-permeability strength | Gas species, pressure, wall thickness and permissible permeation rate still matter. |
| Selected dilute acids | Often suitable / verify | Acid type, concentration and temperature can change results. |
| Selected alkalis | Often suitable / verify | Check chemical identity, concentration, temperature and compound formulation. |
| Petroleum oils & lubricants | Usually not preferred | Swelling and softening risk often makes NBR, HNBR or FKM a better starting point. |
| Gasoline / hydrocarbon fuels | Usually not preferred | Do not select IIR only for “gas sealing” if the gas is a hydrocarbon fuel. |
| Many hydrocarbon / organic solvents | High caution | Solvent exposure can cause swelling or loss of properties; test the actual medium. |
| Ozone & outdoor atmosphere | Strong starting point | Compound formulation and mechanical stress still influence field aging. |
Material Selection
IIR vs. EPDM, NBR, CR, Silicone and FKM: Which Rubber Should You Use?
Choose IIR when its barrier and damping strengths solve the application. Choose another elastomer when oil/fuel resistance, high rebound, extreme temperature or another requirement is more important.
| Material | Where It Can Be a Stronger Starting Point | Main Question vs. IIR |
|---|---|---|
| IIR / Butyl | Low gas/moisture permeability, damping, weathering and selected water/chemical applications | Is barrier performance or damping a primary requirement? |
| EPDM | Outdoor sealing, water, steam/glycol service with a suitable compound, flexible extrusions | Do you need very low gas permeability, or mainly environmental/water resistance? |
| NBR | Petroleum oils, fuels and many industrial oil seals at moderate temperatures | Is oil/fuel resistance more important than ozone/weathering and low gas permeability? |
| CR / Neoprene | Balanced weathering, moderate oil resistance and mechanical performance | Would a balanced general-purpose profile be more useful than IIR's barrier/damping strengths? |
| Silicone / VMQ | Very broad temperature flexibility, clean-color options and selected food/medical formulations | Is low permeability essential, or are temperature flexibility and cleanliness more important? |
| FKM | Higher-temperature hydrocarbon oils, fuels and many demanding chemicals | Does the service medium rule out IIR despite its barrier performance? |
Industrial Uses
Where Is Butyl Rubber Used?
IIR and halobutyl materials are used where gas or moisture retention, damping, environmental aging resistance, resealing behavior or compatible chemical service matters. The exact grade depends on the product construction and qualification requirements.
Air-Retention Components
Inner tubes, tire inner-liner systems, inflatable bladders and other components that benefit from low gas permeability.
Membranes & Bladders
Flexible barriers and pressure-related parts where low permeation and environmental resistance are important.
Seals & Gaskets
Static or low-movement sealing applications involving compatible gases, water, atmospheric exposure or selected chemicals.
Damping Components
Mounts, pads and isolating parts that use IIR's high damping and low rebound to absorb vibration energy.
Hoses, Linings & Barriers
Selected hose layers, tank linings, membranes and barrier constructions where the contacted media are compatible.
Pharmaceutical Closures
Specially formulated halobutyl compounds are widely used for pharmaceutical stoppers and closures, but medical/pharma suitability must be confirmed for the exact grade and application.
Compression & Failure Analysis
Why Do Butyl Rubber Parts Swell, Set, Crack, Tear or Lose Air?
An IIR part can fail because the material is wrong for the fluid, the compound is wrong for the temperature, the geometry creates excessive strain, cure is inconsistent, or the real permeation target was never defined. Visual failure mode and service history should be reviewed together.
| Observed Problem | Possible Mechanisms | What to Check |
|---|---|---|
| Swelling / softening | Hydrocarbon oil, fuel or solvent incompatibility; excessive temperature | Exact media, concentration, volume change, hardness change and exposure time |
| Permanent flattening / leakage | Compression set, excessive squeeze, thermal aging or cure-state issue | Seal compression, temperature/time, cure control and compression-set requirement |
| Loss of air / gas | Wall too thin, pinhole, seam/bond defect, wrong material, excessive permeation or assembly leak | Leak path, wall thickness, pressure, gas species, compound and permeability target |
| Cracking / hardening | Heat aging, chemical attack, overstrain or incompatible service conditions | Temperature history, chemical exposure, strain and aged physical properties |
| Tearing at edges | Sharp geometry, excessive stretch, molding defect or assembly damage | Corner radius, elongation demand, flash/parting line and installation method |
| Bond or layer separation | Poor adhesion, incompatible layers, contamination or insufficient co-cure | Substrate preparation, adhesive system, CIIR/BIIR choice and vulcanization process |
| Dimensional drift | Compound variation, cure variation, shrinkage or measurement method | Production batch, conditioning, datum, measuring force and tooling history |
Custom Manufacturing
How Are Custom Butyl Rubber Parts Manufactured?
IIR, CIIR and BIIR compounds can be processed into molded, extruded, calendered, bonded and multi-layer rubber products. The chosen grade and cure system affect mixing, tack, flow, vulcanization, bonding and dimensional stability.
- Review the function. Confirm gas/liquid media, temperature, pressure, permeation target, movement, service life and failure risk.
- Select the material family. Decide whether regular IIR, CIIR or BIIR is the better starting point and define hardness and required properties.
- Review geometry and tooling. Identify wall thickness, parting lines, gates, flash, bonded layers, undercuts, sealing surfaces and measurement datums.
- Develop samples. Produce samples using the intended compound, cure process and any bonding or reinforcement structure.
- Validate function. Check dimensions, hardness, appearance and application-specific permeability, compression, fluid or aging tests.
- Control production. Maintain compound traceability, cure conditions, inspection criteria and batch consistency.
Compression Molding
Suitable for many custom gaskets, membranes, pads, stoppers and molded parts where part geometry and production volume fit the process.
Transfer / Injection Molding
Can support repeatable production of selected geometries when the compound, cure behavior, gating and tooling are designed for the process.
Extrusion
Selected butyl compounds can be extruded into profiles, tubing or layers. Dimensional stability and cure need process-specific development.
Calendering / Sheet
Butyl rubber can be processed into sheets or barrier layers for lining, membrane and laminated-product applications.
Bonding & Multi-Layer Parts
Halobutyl materials can be useful where compatibility and co-vulcanization with other rubber layers are important. Adhesion must be validated on the actual construction.
Deflashing & Inspection
Finishing method should match geometry and sealing surfaces. Flash, gate vestige, surface defects and dimensional tolerances should be controlled separately.
Dimensions & Tooling
What Tolerances Can Be Achieved on Butyl Rubber Parts?
Tolerance capability depends on part geometry, process, mold design, compound shrinkage, cure conditions and measurement method. Rubber dimensions should be controlled according to function rather than by copying machining tolerances.
ISO 3302-1:2014, confirmed current in 2024, provides dimensional tolerance classes for molded, extruded and calendered solid rubber products when applicable. It does not apply to precision toroidal sealing rings, so O-rings should follow the drawing and an applicable O-ring standard such as ISO 3601 when required.
Identify Critical Dimensions
Separate sealing height, wall thickness, diameters, port interfaces and bonded areas from cosmetic or noncritical dimensions.
Account for Compound Shrinkage
IIR shrinkage can change with compound and cure process. Production tooling should be developed around the selected compound rather than a generic material assumption.
Define Flash Separately
Parting line, flash extension, gate vestige and trimming acceptance are not equivalent to dimensional tolerance.
Agree the Measurement Method
Soft rubber deforms under measuring force. Define conditioning, fixture, datum and measurement method for critical flexible features.
Validation
Which Tests Should Be Specified for Butyl Rubber?
Test selection should follow the real failure risk. For an IIR barrier part, permeability or leak testing can be more important than hardness alone; for a compressed seal, compression set and media exposure may matter more.
| Test Area | Relevant Standard / Method | What It Helps Verify |
|---|---|---|
| Shore hardness | ISO 48-4:2018 or agreed equivalent | Indentation hardness of the specified compound |
| Tensile / elongation | ISO 37:2024 or agreed equivalent | Strength and elongation before and, when required, after aging |
| Compression set | ISO 815-1:2019 or agreed equivalent | Elastic recovery after prolonged compression under defined conditions |
| Fluid immersion | ISO 1817:2024 or customer-defined method | Volume, mass, hardness and property changes after liquid exposure |
| Gas permeability / air retention | Application-specific method | Whether the compound or finished part meets the required barrier performance |
| Leak / pressure retention | Part-specific functional test | Assembly leakage, pinholes, bond integrity and pressure-holding function |
| Heat / aging | Customer specification or applicable rubber-aging method | Change in hardness, tensile, elongation, appearance or function after aging |
| Dimensions / visual quality | Approved part specification and inspection plan | CTQ dimensions, flash, surface defects and batch consistency |
Test edition, specimen geometry, exposure time, temperature, pressure, permissible leak/permeation rate and acceptance limits should be agreed for the project. Standards listed here do not constitute a certification claim for a supplied part.
Regulatory & Specification Boundary
Does Butyl Rubber Automatically Meet Food, Medical or Pharmaceutical Requirements?
No. IIR, CIIR or BIIR describes a polymer family, not a regulatory approval. Although specially formulated halobutyl compounds are widely used in pharmaceutical closures, a generic butyl compound cannot be assumed to meet a medical, food-contact, drinking-water, pharmaceutical or customer-specific requirement.
- State the exact regulation, pharmacopeial requirement, customer standard or approval needed.
- Confirm whether the requirement applies to raw polymer, finished compound, finished component or complete closure system.
- Define extractables/leachables, cleanliness or drug-contact requirements when they apply to the project.
- Confirm color and formulation because fillers, curatives, plasticizers and process aids can affect compliance.
- Request the required document type: declaration, test report, material certificate or third-party approval.
- For RoHS, REACH or other substance requirements, confirm the exact compound and reporting scope.
RFQ Preparation
What Information Should You Send for a Butyl Rubber RFQ?
A useful IIR RFQ defines both geometry and barrier/service requirements. This makes it possible to review material selection, tooling and validation before production assumptions are locked.
| RFQ Item | Information to Provide | Why It Matters |
|---|---|---|
| Part definition | 2D dimensions, 3D file or physical sample | Defines geometry, tooling, CTQ dimensions and manufacturing process |
| Function | Seal, membrane, bladder, damping part, hose layer, bonded part, stopper, etc. | Changes mechanical, barrier and material priorities |
| Gas / liquid media | Exact gas, water, chemical, oil, fuel or mixture; concentration if known | Separates suitable barrier service from incompatible hydrocarbon exposure |
| Permeation / leak target | Permissible leak rate, pressure loss or transmission requirement when applicable | Turns “airtight” into a measurable functional requirement |
| Temperature | Minimum, continuous and peak values plus peak duration | Supports aging and low-temperature review |
| Pressure / vacuum | Normal, maximum and cycling conditions | Affects wall design, sealing load, permeation and fatigue |
| Hardness | Target Shore A and tolerance if specified | Affects compression, deformation and damping |
| Material requirement | IIR, CIIR, BIIR, approved compound or performance specification | Prevents substitution and cure/compatibility misunderstandings |
| Compliance | Exact regulation, test report, pharmacopeial or customer requirement | Butyl polymer identity alone does not prove compliance |
| Quantity | Prototype quantity, order quantity and expected annual usage | Supports tooling and process selection; MOQ and lead time can then be confirmed |
| Existing failure | Photos, returned parts and known swelling, leakage, set or bond issues | Helps separate material, geometry, assembly and processing causes |
Butyl Rubber FAQ
Frequently Asked Questions About Butyl Rubber (IIR)
What does IIR stand for?
IIR is the standard abbreviation used for butyl rubber, an isobutylene-isoprene copolymer. It identifies the polymer family but does not by itself define hardness, cure system, formulation or finished-part properties.
Is butyl rubber airtight?
Butyl rubber has very low gas permeability and excellent air-retention capability compared with many common elastomers, but no practical rubber part should be described as absolutely impermeable. Gas species, pressure, wall thickness, compound and assembly leakage all affect the result.
What is the difference between IIR, CIIR and BIIR?
IIR is regular butyl rubber. CIIR is chlorobutyl and BIIR is bromobutyl. Halogenation increases cure reactivity and improves compatibility/co-vulcanization options with other diene rubbers, which can be valuable in multi-layer products.
Is butyl rubber resistant to ozone and weathering?
IIR is generally a strong material family for ozone, atmospheric aging and weathering resistance. The final part still needs the correct formulation and design for its outdoor load, temperature and service life.
Is butyl rubber resistant to water?
Water and moisture resistance are important strengths of IIR, but hot water, additives, treatment chemicals and pressure/temperature conditions should be included in compound validation.
Is butyl rubber oil resistant?
Butyl rubber is generally not the first choice for petroleum oils and hydrocarbon lubricants. NBR, HNBR or FKM may be stronger starting points depending on oil type and temperature. Verify the actual fluid before selecting the material.
Can IIR be used with gasoline or diesel fuel?
IIR is generally not preferred for continuous contact with hydrocarbon fuels. Its excellent air/gas barrier behavior should not be confused with fuel resistance. NBR, FKM or another compatible material may be more appropriate.
Why is butyl rubber used for vibration damping?
IIR dissipates mechanical energy effectively and has relatively low rebound. That makes it useful for pads, mounts and other components where vibration absorption matters more than high resilience.
What temperature can butyl rubber withstand?
There is no single guaranteed temperature range for all IIR compounds. State the minimum, continuous and peak temperatures, plus service media and duration, so the proposed compound can be checked for the actual application.
IIR or EPDM: which should I choose?
Both can be useful for weathering and water-related applications. IIR becomes especially attractive when very low gas/moisture permeability or strong damping is needed. EPDM may be preferable for many outdoor, water, glycol or extrusion applications. The exact media and function decide.
IIR or NBR: which should I choose?
Choose IIR as a starting point for low permeability, damping, weathering and compatible water/chemical service. Choose NBR as a starting point when petroleum oil and fuel resistance is the dominant requirement at an appropriate temperature.
Can butyl rubber be used for pharmaceutical stoppers?
Specially formulated halobutyl compounds are widely used for pharmaceutical closures, but generic CIIR or BIIR is not automatically pharmaceutical grade. Drug compatibility, extractables/leachables, cleanliness, applicable pharmacopeial requirements and the complete closure system must be validated.
Does black IIR automatically meet FDA, REACH or RoHS requirements?
No. Color and polymer family do not prove compliance. The exact compound, applicable regulation, reporting scope and required documentation must be confirmed.
Can butyl rubber be bonded to metal or other rubber?
Yes, selected IIR/halobutyl compounds can be used in bonded or multi-layer constructions. Substrate preparation, adhesive or co-vulcanization system, cure conditions and service environment must be validated for the actual design.
What information is needed to quote a custom IIR part?
Send part dimensions or 3D data, function, gas or liquid media, minimum/continuous/peak temperatures, pressure or vacuum, required leak/permeation performance, hardness if specified, compliance requirements and quantity. A physical sample and failure photos are useful when replacing an existing part.
Custom Butyl Rubber Manufacturing
Have an IIR seal, membrane, bladder, gasket or molded part to develop?
Send the part geometry, gas or liquid media, operating temperatures, pressure, permeation or leak requirement, hardness or material requirement and expected quantity. We can review the information needed to confirm compound selection, tooling and manufacturing feasibility.