What is the plastic film in my door?

During the cold weather months, windows become a prime spot for energy loss. Duck Max Strength Brand Rolled Window Insulation Kits feature a

Duck Brand 84 x 120 Rolled Shrink Film Window Kit, Fits Patio Doors or XL Windows

A footprint just appeared on my window's plastic cover. : r/Weird

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Duck 286218 Extra Large Patio Door Shrink Film Window insulation

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