Bromobutyl vs Chlorobutyl Vial Stoppers
Worldwide sales of chlorobutyl and bromobutyl vial stoppers from IVPACKS LLC


In the US and European markets, serum vial stoppers are commonly available in both bromobutyl and chlorobutyl rubber for use in pharmaceutical packaging. Vulcanization (heating and curing) of natural rubber results in the cross-linking of individual polymer chains that forms a copolymer of isobutylene, and to a smaller extent, isoprene. The incorporation of a halogen (bromine or chlorine) in the vulcanization process results in the vulcanization rate being improved, blending and curing performance is improved, and the cross-link bonding property has also significantly improved. Each specific halogen offers its own unique characteristics to the finished product.

Bromobutyl Rubber: is a terpolymer of isobutylene, isoprene and brominated Isoprene.

Chlorobutyl Rubber: is a terpolymer of isobutylene, isoprene and chlorinated Isoprene.

Processing with Bromobutyl vs Chlorobutyl

  • When bromine is used as the halogen for producing bromobutyl rubber, it is generally added at a concentration of 2%; chlorine is added at a concentration of 1.1 – 1.5% in chlorobutyl rubber.
  • Bromine is more reactive than Chlorine, so a stabilizer is often added to the rubber (such as soybean oil at 1.3%). Chlorine, being more inert, does not require the use of any stabilizers.
  • The use of antioxidants (such as BHT) is approximately equal in both bromobutyl rubber and chlorobutyl rubber.

Advantages and Disadvantages: Bromobutyl vs Chlorobutyl

Bromobutyl Rubber


  • lower hygroscopicity and is a better choice for freeze dried / lyophilization product applications. Higher stability and generally have a longer shelf life.
  • faster cure rates and a shorter scorch or cure induction period (more efficient production)
  • requires lower levels of curatives and enables one to use a wider range of accelerators.


  • stabilizers are required in the production of bromobutyl rubber (such as soybean oil).
  • heat sensitivity is a greater concern with bromobutyl stoppers.

Chlorobutyl Rubber


  • better resistance to heat and is the preferred stopper for high-heat sterilization techniques.
  • efficiently produced without the use of stabilizers.


  • longer curing times, resulting in higher production costs