What’s the advantage of putting plastic film on the windows in winter?
Plastic film is the most helpful for windows that are old or in bad condition. If installed properly, putting plastic film over a window is almost equivalent to adding an extra pane of glass on the window. This could mean up to a 50 percent decrease in heat loss through the glass, but little or no reduction in heat loss through the window frame. So the better your windows, the less benefit you’ll get from plastic films.
Applying a plastic layer can actually decrease condensation (one of the few interior window treatments that doesn’t cause moisture problems). Although the film cools the surface temperature of the glass, it also acts as a vapor barrier and prevents large amounts of warm, moist air from reaching the cooler glass. If you can see a haze or droplets of water near the bottom of your windows, that’s a sign that your windows could use an upgrade or that the humidity in your house is too high.
The plastic film can also improve comfort in the home by reducing drafts that form when air is cooled by the window’s surface. If positioned well, plastic films can sometimes be used to help reduce cold air coming in past window edges and seals.
All of these benefits rely on proper installation. The common plastic films available at the grocery or hardware store do not insulate by themselves, but instead add insulation by trapping air between the glass and the plastic film. The optimal air gap to create is between 3/8 and 3/4 of an inch. The double sticky tape must be sealed continuously and smoothly to the window frame surface in order to trap air effectively; otherwise, air and water vapor will sneak through, which becomes quickly apparent as condensation builds up behind the plastic.
Be sure to use plastic on widows that house pets and children can’t access, because puncturing the plastic will ruin it. Unfortunately, covering windows with plastic limits visibility somewhat, depending on the quality of the installation and the lighting. The finishing touches are achieved by blowing a hair dryer on the plastic to tighten it and smooth out the wrinkles. This part is crucial to getting the best light transmittance, so take your time and work carefully.