Window insulation film is a clear plastic sheet you tape over the interior of a window and then shrink tight with a hair dryer. It creates an air pocket between the film and the glass that acts as an extra layer of insulation. It takes about fifteen minutes per window and costs roughly five dollars per window.

I put it on three drafty windows in my living room last winter. The room was noticeably warmer the next morning — not “turn off the heat” warmer, but “my feet aren’t cold on the floor” warmer. That air pocket does real work.

What you need

A window insulation kit from any hardware store. It comes with the plastic film and double-sided tape. You also need a hair dryer and scissors. That’s everything.

Installation

1. Clean the window frame. The tape won’t stick to dust or condensation. Wipe it dry with a cloth. If the frame is cold, warm it slightly with the hair dryer first — tape adheres better to a warm surface.
2. Apply the double-sided tape. Stick it around the entire perimeter of the window frame, not the glass. Press it down firmly along the full length.
3. Cut the film. Unroll the plastic and cut it about two inches larger than the window on all sides. Bigger is better — you’ll trim the excess later.
4. Attach the film. Starting at the top corners, press the film onto the tape. Don’t stretch it yet. Just get it stuck all the way around. Let it be slightly loose.
5. Shrink it. This is the satisfying part. Use the hair dryer on high heat about six inches from the film. Move it back and forth. The wrinkles will disappear and the film will pull tight as a drum. Don’t hold the dryer in one spot too long or you’ll melt a hole.
6. Trim the excess. Run a utility knife along the edge of the tape to remove the extra film.

Take the film down in the spring. It peels off and the tape removes cleanly from most surfaces. If there’s residue, a little rubbing alcohol takes it off.

Which windows need it most

Prioritize north-facing windows and any window you can feel a draft from. Single-pane windows benefit the most. If you have modern double-pane windows that are already sealed well, you probably don’t need the film.

One kit covered three average-sized windows for me. Your mileage depends on window size. But even for big picture windows, a couple of kits is still cheaper than one month of a higher heating bill.