DIY insulating window films

Where there's no double- or triple-glazing, do-it-yourself plastic film insulation kits are often suggested as a cost-effective way to insulate windows against heat loss and to save on energy costs.

Plastic film is taped to the edge of the window frame, and a hair dryer is used to shrink-wrap the film tight across the frame. The hair-dryer trick is definitely the fun bit.

It sounds easy enough. It certainly looks a doddle on YouTube.

But are these kits simple to install – or effective? I decided to give it a go.

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Collect the materials you need: kits, measuring tape, scissors, cleaning gear and a hair dryer.

You need a window frame you can stick tape to without damage. Using the tape on veneer panelling, painted plasterboard or wallpaper is not recommended. If the tape lifts paint from the window frame surface that's a consideration, especially when renting. According to government agency GenLess, the tape won't stick to aluminium joinery.

Bear in mind that once the film is applied, it allows sunlight in (unlike thick curtains), but you may not see out the windows as well. You also won't be able to open the window, or use the window sill.

If the film gets punctured you lose the essential insulating air gap.

According to one brand video, there's "an extreme version, which is a thicker more durable film if you have small kids or pets who like to press their faces up against your windows and doors."

This conjures all kinds of problematic scenarios. I can't help wondering about the chances of the plastic film against small sticky fingers, scratchy claws – or the freaky things that happen with dog or cat hair and static electricity.

First up, I needed a hair dryer, as having curly hair I’ve never owned such a gadget. A few days and $25 later, a second-hand model arrives at my door.

Measure your windows and compare with kit dimensions, allowing extra film for trimming.

After a trip to a local hardware store I have two kits: Polar Bear Weatherproofing, $16.98 (3 sheets at 92cm x 1.5m) and 3M Window insulator Kit $15.19 (2 sheets at .91m x 1.52m).

Before starting each window and frame needs a decent clean, to avoid any dust or dead spiders being entombed behind the film.

The double-sided tape is applied around the window frame, leaving no gaps. While the tape adhesive is setting, lay out your film and cut it to shape, leaving some excess around the edges.

If you have pets or your house is any way dusty (like mine) I suggest first laying out a clean bedsheet.

According to the video, all that's needed is to then hold the film by the top corners, pull it taut and apply it to the top, then the bottom, then the sides of the frame.

"Don't worry, if it's not perfect, You can adjust the film. Take your fingers and gently press on the tape, to secure the film," they say.

What actually happens is bits of the film get stuck in the wrong bits of the tape. Instead of being easy to "adjust" it peels off the frame while resolutely sticking to the film. After some faffing and extra lengths of tape, the film is finally stretched across the window, including a few wrinkles.

Wrinkles might look bad, but what's more crucial at this point, is that the window is dry inside and there are no air gaps. A study by Branz analysing different types of window films, found that "performance is lost if there is condensation on the glazing."

After all that, using the hairdryer to tighten the film is really very satisfying. It considerably smooths the wrinkles. Unfortunately any creases and other snafus stuck in the tape will likely stay put, and can look disappointingly messy.

Carefully trimming the excess around the edges can improve things a bit.

Maybe it's a bit ambitious to try doing this alone. Having successfully wallpapered and put up window frosting in the past, I found this project surprisingly tricky.

One suggestion is that you can save the pieces to use again next winter. This sounds great, saving money and extra plastic. I wonder how many films are successfully reused in this way.

Aesthetics aside, is it effective?

My initial idea was to use a thermometer to measure any change in room temperature before and after. But by the time I’d completed the installation, the sun had dropped, taking the temperature outside with it and rendering any measurements invalid. I was warm meanwhile – possibly even a bit hot and bothered.

On the technical front, the answer is yes. The Branz window film study found that in some instances plastic window films could increase heat retention by up to 40%.

Now that's an impressive result for the cost of a few kits, a few hours and a hairdryer.

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