One of the few external rigid points on the GZ-20’s envelope, it holds the battens, attachments for the nose lines and the mooring spindle. 2. Material. The largest component of the Blimp, the GZ-20’s envelope is made of two-ply, neoprene-impregnated polyester fabric. 3. Ballonet. Located in the forward and aft of the envelope, these air bags allow the pilot to regulate the amount of helium in the Blimp and statically trim the ship in a nose-up or nose-down situation.