The Underwriters Laboratories is an organization that has established standards for elastomeric compounds in specific service environments. In order to display the UL trademark label, annual tests must be performed to ensure that the compounds will exceed the conditions they normally encounter.
Apple Rubber has a variety of compounds listed by UL of applications such as propane, natural gas and heating oils. Apple Rubber routinely submits new compounds for UL approval in different service environments.
If you want a UL-registered compound, you must be sure to specify it.