Well, let’s see: https://en.wikipedia.org/wiki/Film_capacitor AND: https://eepower.com/capacitor-guide/types/film-capacitor/# Google Search, to the rescue!
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Though the vast majority of film caps are nonpolar, noise is a concern in audio circuits. I’ve always tested mine (by ear or scope), to predetermine installation orientation. https://www.aikenamps.com/index.php/where-to-connect-the-outside-foil-on-capacitors
"Poly" just means synthetic polymer. Film or Foil? Foil capacitors are made with metal foils (usually aluminium) separated by layer of dielectric while Film capacitors are made with metallized layers on dielectric films. Film capacitors are smaller but Foil capacitors offer larger current capabilities. Polypropylene capacitors have lower dielectric constant and better high frequency characteristics, but are larger and more expensive than polyester. Any Poly capacitor will be better than electrolytic (but much larger). Poly caps are non-polarized, but one side is usually marked with a bar. This is the end of the outer layer. Connecting this side to GND provides shielding.