This is a set of 4 double FEP films for the Zortrax Inkspire 3D printer.  The FEP film is the double-layered transparent foil that allows UV light to pass through it and cure the resin.  It is installed in the rack attached to the 3D printer's resin tank.  Once the FEP film becomes bent, deformed, or perforated, it must be replaced to ensure the Inkspire printer produces the best possible 3D printed models.