Well, a layer of Polymer-Dispersed Liquid Crystals is sandwiched between two transparent thin layers of conductive film material.

A busbar (conductive copper strip) is attached to one end of the cut-to-size film. Wires are attached to this strip for the power source to activate the liquid crystals within the film.

This film, in turn, is sandwiched (laminated) between two sheets of glass.

Power activates the crystals, aligning them to enable transparency through the film, and therefore, through the glass.

Turning the power off sets the liquid crystals into unaligned positions therefore making the film (and glass) obscure.

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