Are Mylar Balloons made of DuraLar? No! Mylar Balloons are not made of any type of DuraLar, or Mylar or any other type of Polyester Film. ” Mylar balloons ” are made of a specially coated Nylon designed to seal to itself, and act as a barrier to hold helium gas. Unfortunately, we do not supply any material that is acceptable for this application. Any film that we would sell you, would not be able to hold the helium gas long enough to make it worth while!