Orientations in PET films

Viewing it through crossed polars would work qualitatively, and then inserting a 1/4 wavelength plate would let you quantify it using Babinet or Senarmont compensation. You could also use x-ray diffraction.

John Aspen Research, -

Opinions expressed herein are my own and may not represent those of my employer.

As John says, crossed polars should work. I know that Mylar PET film is biaxially oriented. Don't know how it would look under crossed polars. I would assume film for use as is, is biaxially oriented. Film extruded for subsequent thermoforming is unoriented or maybe slightly oriented in the extrusion direction. Snipping small pieces and cold drawing by hand might indicate orientation too. Frank

Thank you very much for the quick answers!