Butyl (IIR)

Butyl Rubber (IIR) Overview

Butyl rubber is a synthetic elastomer produced by copolymerising isobutylene with a small proportion of isoprene. In industry-standard nomenclature it is designated IIR under ASTM D1418.

Traditionally used for sealing and gasketing, Butyl has in many cases been replaced by alternatives such as EPDM. It still offers a distinctive mix of properties that make it valuable in specialist sealing duties where airtightness, environmental resistance, and vibration damping matter most.

Standard appearance is typically a black rubber compound.

Why Use Butyl

Butyl remains a strong choice for sealing, gasketing, and damping applications because of several core performance characteristics:

• Exceptional impermeability to gases and vapours — Butyl has extremely low gas permeability, making it well suited to airtight and vacuum-seal applications such as vacuum systems, compressed-air or gas sealing, and pneumatic or vacuum pipelines.
• Resistance to UV, ozone, and weathering — It resists degradation caused by sunlight, ozone exposure, and environmental ageing, which supports both indoor and outdoor use.
• Shock, vibration, and sound damping — Its low resilience and viscoelastic nature help absorb mechanical shock and reduce vibration, making it useful in hydraulic sealing and vibration-isolating components.
• Broad service temperature capability — Typical grades can operate from around -40°C up to between +100°C and +140°C depending on the specific compound and product form.
• Selective resistance to chemicals and synthetic fluids — Butyl performs well against certain polar solvents and synthetic fluids where mineral oils and aggressive hydrocarbons are not present.

Typical Applications & Use Cases

Given these properties, Butyl is often specified for:

• Vacuum sealing and compressed-gas sealing in vacuum systems, compressed air or gas pipelines, pressure vessels, and pneumatic equipment.
• Hydraulic systems using synthetic fluids or other non-mineral oils, where Butyl O-rings, seals, or gaskets can operate without exposure to mineral oils or aggressive hydrocarbons.
• Gaskets and washers where low gas permeability or airtight sealing is required.
• Shock and vibration damping components such as bushings, mounts, pads, and vibration-absorbing gaskets.
• Sealing and waterproofing applications exposed to weather, moisture, UV, or outdoor conditions.

Typical Specification Range

A common reference grade is Butyl 70, though actual values depend on the exact formulation supplied.

As with all elastomers, the usable temperature range depends on compound specifics, age, environment, exposure conditions, and seal design.

How Butyl Compares with Alternative Materials

Compared with many general-purpose rubbers such as natural rubber or standard nitrile, Butyl’s main advantage lies in its gas impermeability, weathering resistance, and shock or vibration damping.

If the application involves oils, fuels, mineral-based lubricants, hydrocarbon solvents, or aggressive petroleum media, more oil-resistant elastomers such as nitrile-based or fluorocarbon-based materials are often better choices.

Halogenated Butyl grades have been developed to improve oil and chemical resistance. Chlorobutyl and bromobutyl compounds offer better performance in these environments than standard Butyl and are also widely accepted in pharmaceutical and medical stopper or septum applications.

When to Choose Butyl

Choose Butyl when the application depends on:

• Airtight or gas-tight sealing for vacuum systems, gas retention, or compressed-air lines.
• Long-term resistance to ozone, UV, weather, or outdoor exposure.
• Shock absorption, vibration damping, or noise reduction in dynamic equipment.
• Compatibility with polar solvents, synthetic fluids, or mild chemicals rather than petroleum-based media.

If the duty involves regular exposure to oils, fuels, hydrocarbon solvents, or diester-based lubricants, choose a more oil-resistant alternative or consider a halogenated Butyl grade where appropriate.

Compliance & Quality Considerations

At Eastern Seals (UK) Ltd, Butyl compounds are sourced from certified manufacturers. Because approved supply may come from more than one source, the exact compound batch, hardness, or performance profile can vary.

The information provided on this page should therefore be used as a guide only. Purchasers should verify compatibility and performance against their specific application requirements, particularly for critical sealing duties.

Looking for an alternative style? Contact our Sales team.

Butyl is a petroleum-derived material, but it has poor resistance to hydrocarbon solvents, mineral oils, and diester-based lubricants. Verify media compatibility before specifying it in any oil-exposed sealing system.