Rubber vs Butyl Rubber (IIR): Key Differences Explained
Rubber is a broad category of high-elastic polymer materials capable of undergoing large deformation under external force and returning to their original shape once the force is removed. Rubber materials are mainly divided into natural rubber (NR)-derived from natural rubber latex-and synthetic rubber, which is produced through chemical polymerization processes.
Butyl Rubber (IIR) is one of the most important types of synthetic rubber and is widely used in applications where airtightness and durability are critical.
The core differences between butyl rubber and other rubbers lie in their chemical structure, performance characteristics, and application focus.
Chemical Structure Differences
Butyl rubber (IIR) is a copolymer of isobutylene with a small amount of isoprene. Its molecular backbone is predominantly composed of saturated carbon–carbon bonds, with only a very low level of isolated double bonds.
In contrast, natural rubber (cis-1,4-polyisoprene) and many other synthetic rubbers-such as styrene-butadiene rubber (SBR) and butadiene rubber (BR)-contain a high concentration of unsaturated conjugated double bonds in their molecular chains.
This highly saturated structure is the fundamental reason behind the excellent air impermeability, aging resistance, and chemical stability of butyl rubber (IIR).
Performance Differences
Air Impermeability
Air retention is the most outstanding property of Butyl Rubber (IIR). Its air permeability is only 1/10 to 1/20 that of natural rubber, making it the best airtight rubber material available. This is why IIR is the preferred choice for products requiring strict sealing performance.
Aging and Weather Resistance
Thanks to its saturated backbone, butyl rubber is highly resistant to ozone, UV radiation, and thermal aging. Its ozone crack resistance is over 10 times better than natural rubber, and it performs reliably within a long-term temperature range of –40°C to 120°C.
Elasticity and Processability
Butyl rubber has lower elastic recovery compared with natural rubber and BR. Its rebound resilience is approximately 60%–75%, while natural rubber typically reaches 85%–90%. In addition, IIR rubber compounds have high molecular weight and require higher mixing temperatures (120–150°C), resulting in more difficult processing, higher energy consumption, and slower vulcanization speed.
Cost
Due to its complex low-temperature cationic polymerization process, the production cost of butyl rubber (IIR) is generally 30%–50% higher than natural rubber.
Main Application
Based on its unique performance profile, Butyl Rubber (IIR) is mainly used in applications that demand excellent airtightness, aging resistance, and chemical stability, while natural rubber and other elastomers are preferred for high-elasticity or wear-resistant applications.
Butyl Rubber (IIR) Applications
- Tire inner tubes and inner liners
- Pharmaceutical rubber stoppers
- Automotive door and window sealing systems
- Building waterproof membranes
- Chemical equipment gaskets and seals
Natural Rubber (NR) Applications
- Tire treads requiring high elasticity
- Rubber footwear
- Medical and consumer products such as condoms
Other Synthetic Rubbers
- SBR (Styrene-Butadiene Rubber): tire treads (wear resistance, cost efficiency)
- BR (Butadiene Rubber): tire treads and shoe soles (elasticity and light weight)