PE film is Cheep! Hdwr stores sell it as painters' dropcloth. It is smooth and slippery and doesn't hold glue or tape well, making it somewhat difficult to fabricate into an airship envelope or lift bag.
Some constructors "flash" the PE surface with a soft flame to prepare it for glueing.
Other wipe it with a "primer", mostly containing acetone, to remove any "mold release" from the surface before gluing.