What is Butyl

What is Butyl?

Butyl is produced by copolymerizing isobutylene with small amounts of isoprene (typically 98% polyisobutylene and 2% isoprene). Butyl rubber was first commercialized in the early 1940s. With excellent gas impermeability and air retention along with good flex properties, the first major application of butyl rubber was tire inner tubes.

Butyl rubber has a typical service temperature range between –75° F and +250° F.


Butyl rubber has exceptional resistance to gas and moisture (water and steam) permeation. Butyl rubber also has excellent resistance to oxygenated solvents (ketones and alcohols), alkalis, flexing, and abrasion. Butyl is capable of providing high energy absorption (damping) and thus has excellent electrical isolation performance. Butyl has good resistance to sunlight, ozone, heat aging, animal and vegetable oils, oxidizing chemicals, silicone fluids and greases, ammonia, hydrazine, and phosphate ester type hydraulic fluids (e.g., Skydol, Fyrqeul, Pydraul).

The molecular structure of butyl rubber can be oriented to resist stress. Mechanical properties are retained over a relatively wide stiffness range since reinforcement is not required for good tensile and tear strength.


Butyl rubber is difficult to handle during manufacturing because of its tendency to trap air, blister, and creep. Cold flow characteristics and flame resistance are poor. Butyl is not recommended for use with petroleum oils, fluids, or solvents. Butyl has poor resistance to aromatic hydrocarbons (e.g., Benzol, Toloul), aliphatic hydrocarbons (e.g., kerosene, turpentine), coal, tar, and diesterbased lubricants. Cold weather properties for butyl rubber are fair.


Butyl’s excellent impermeability to gas makes it very useful in seals for vacuum applications. Butyl’s gas impermeability coupled with its air retention capabilities make butyl popular for use in tire inner liners and inner tubes. Butyl is also used in hydraulics applications where synthetic fluids are used.