Generally, the EWF method is applied to the characterization of polymer sheets of little thickness (t < 2 mm). In the present study,the selected material is an amorphous polyethylene terephthalate
(A-PET) manufactured by extrusion, type A-B-A 100% (layers A of 100% virgin material and layer B of recovered materials) whose theoretical weight is 1 :33 gr=cm3 and with an initial extruded
sheet thickness of 0:492 mm.