When searching for a chemical resistant o-ring, gasket, or seal, the most successful elastomers will be in the class of fluorocarbon rubbers. Several characteristics of  fluorocarbon rubber tend to impart the characteristics necessary for chemical resistance, specifically,

• the ratio of fluorine to hydrogen,
• the inherent strength of the carbon-fluorine bond,
• the absence of carbon bond unsaturation, and
• the steric hindrance associated with fluorinated structures.

As a general rule, the higher the fluorine content, the broader the chemical resistance. However, there are exceptions to this rule that can be attributable to the solubility parameter of a given reagent and the elastomer designated to seal the reagent. Consideration must also be given to the curative employed within the fluorocarbon rubber.

The second rule of thumb is that the higher the fluorine content, the more expensive the polymer will be. But again, exceptions exist. For instance, a Type 2 FKM (such as Viton ® B) possesses a higher Fluorine content than an Aflas ® FEPM, yet the FKM costs less. Generally speaking, FKM's will be the least expensive fluorocarbon elastomer, followed by FEPM, with the most expensive being FFKM. 

Good background information on Fluorocarbon Elastomers can be found in our Technical Papers Online page. For information on base resistance you may want to visit our statement about BREs.