Do window insulation kits work?

Plastic over windows is a common tactic used to reduce drafts and energy waste. But does it actually work?

Plastic over windows is a common tactic used to reduce drafts and energy waste. But does it actually work?

When people ask us if window insulation kits work—you know, those classic shrink-wrapping window kits that are almost the equivalent of grocery-store plastic wrap—it’s immediately clear to us that there’s a bigger underlying problem in their house.

And that problem usually isn’t fixed by using plastic over windows as insulation. Depending on where you live, Sealed can pinpoint the real issue and fix it for $0 upfront if your house qualifies. Find out how.

In this article, you’ll find out why—and you’ll also get answers to the following questions:

Key takeaways in this homeowner guide:

  • If you’re hoping to save money on energy costs, installing window insulation film is certainly more cost-effective than replacing all of your old windows with new ones.
  • Before you head to the hardware store, it’s important to understand that plastic window film doesn’t have a huge impact on your energy bills… and it won’t solve the underlying problem that’s causing heat loss (or heat gain) around your windows.
  • Building science backs this up. And window kit manufacturers claim energy savings may be more dramatic that homeowners actually experience.
  • Thermal window coverings may provide better temporary insulation in most cases.
  • To truly solve the underlying problem, a whole-home approach is needed. Professional air sealing and upgraded insulation is the right fix. 

How window insulation kits work

The idea behind a window insulation kit is to create an airtight seal between your window and the interior of your home. The plastic film creates a trap for the air between your window and the film itself. 

These window plastic kits are easy to install. You cut the plastic to fit your window and use double-sided tape to adhere it across the entire pane. Then, using a hair dryer, shrink-wrap the plastic film to fit snugly across.

Theoretically, this is supposed to reduce cold or hot air that’s outside from entering your house through your windows. Some people refer to putting up a window insulation kit as “winterizing your windows” or “sealing your windows.” 

So do window insulation kits work at all? Why not?

We’ll cut to the chase: No, not really.

To understand why, let’s discuss R-value. 

R-value is the measurement of thermal resistance of a material. Basically, the higher the R-value, the better that material is at stopping hot or cold air from passing through.

Let’s compare a few common materials to see what their R-values are:

  • A standard double-pane window’s approximate R-value is 2 (1).
  • The standard rolled-up batts of fiberglass insulation (typically used in attics) has an R-value of 2 to 2.5 per inch. 
  • An insulated wall has an R-value of 12 to 19. 

But what about window insulation kits? 

Well, a single layer of polyethylene film (which is often used for greenhouse coverage in gardening or farming) has an R-value of approximately 0.85 (2). 

And the sheeting that comes in your plastic window insulation kit is usually much thinner than that.

That’s a disappointing number, especially since these kits are marketed to people as window insulation that will save 30-50% on your energy bills. Maybe technically you can call a thin layer of plastic insulation… but most homeowners won’t see that kind of dramatic reduction in their energy bills—not even close.

But don’t just take our word for it. rates plastic over windows only 2 out of 5 stars for saving energy and money, which is pretty low, considering they give attic air sealing alone 4 out of 5 stars (4, 5).

Window kit manufacturers claim energy savings may be more dramatic that homeowners actually experience.

Whole-house air sealing can reduce your energy use up to 30% (6). And that percentage increases even more when you pair air sealing with insulation and HVAC upgrades. 

(We’ve worked with thousands of homeowners, and we know that, with the right home upgrades, you can reduce your home’s energy use up to 50%.)

So going through the hassle of putting window plastic on every window in your home isn’t going to make a big impact. Not to mention, it doesn’t look too pretty.

Does putting plastic on windows help in the summer?

While window insulation kits are often advertised as a way to reduce heating costs, putting plastic up won’t help in the summer either. In fact, it’s likely you’ll get better results by installing thermal curtains, as they can provide a higher level of window insulation than shrink-wrapping your windows can. 

You can reduce your average utility bills by 15% by upgrading your insulation (including attic insulation) and air sealing your home.

How to improve window insulation

So if window insulation kits won’t significantly reduce drafty windows, what will

Here are five short-term solutions for improving window insulation:

  • Add thermal curtains and blinds. Thermal window coverings may offer a better short-term solution for drafty windows than plastic wrap. To learn more about the efficiency of thermal curtains (and how to install them), read Do thermal curtains work?
  • Install custom-fit window insulation panels. A custom-fit plexiglass window insulation panel (also called window inserts) will provide you with a sturdy, reusable option that provides a tight seal (without all the tape and throw-away plastics). Plexiglass sheets can be purchased at most hardware stores.
  • Update your window weatherstripping. Weatherstripping is a material applied to the edges of windows and doors to create a tight seal. Over time, the weatherstripping wears down. Replacing it is an affordable, easy fix to reduce window drafts. 
  • Reglaze your windows (also called glazing). If you have older single-pane windows or wooden window frames, you may need to reglaze your windows. Reglazing simply means replacing the glass panes with newer ones. This is technical work, as it requires removing the glass from its frame—so make sure to get professional help if you need to.
  • Caulk air leaks around windows. Add a line of caulk to close gaps and reduce unwanted airflow for good—but make sure you don’t block the weep holes. (Weep holes are small, rectangular drainage openings usually found at the bottom of vinyl or metal window frames—they allow rainwater to easily run out of the window, preventing moisture damage.)  

For a more in-depth look at improving window insulation, read the How to Fix Drafty Windows homeowner guide.

An older couple hangs thermal curtain on their windows to reduce drafts.

How to insulate windows from cold 

To insulate your windows against cold temperatures, adding thermal curtains and fresh weatherstripping are solid temporary solutions that you can do yourself in an afternoon. If you own your home, you’ll want to also air seal your windows and determine if you need to reglaze them or consider custom-fitted plexi-glass insulation panels.

Insulating your windows from cold temperatures can be accomplished with the five suggestions listed above. But remember, these alternatives are pretty ineffective when compared to whole-home insulation upgrades and air sealing that can permanently fix drafty house problems. 

If your home struggles to stay warm in cold weather, read Why is my house so cold—and how do I fix it for a comprehensive look at weatherizing your home.

Winter has hardly started and we already feel the difference in the house…. If your house is drafty, go for it with Sealed!

Anita B., Sealed customer

How to insulate windows for summer

The same tactics you use to insulate your windows in winter can be used for the summer, including using thermal curtains to block heat, closing the blinds on hot days, and weatherstripping. 

You can also install solar window film to help block summer heat from coming through your windows. Like regular window insulation kits, solar window film adheres directly to the window glass. It works as a temporary solution to block out UV rays and add a mild layer of heat protection.

For a more effective way to fix hot, uneven temperatures in summer, read Why is my house so hot—and how do I fix it.

This was the SINGLE BEST THING we could have done for our home!!! I’m excited to see how the summer is now that our upstairs isn’t an oven! Thanks so much, Sealed team!!

Liz C., Sealed customer

Does winterizing windows work?

Winterizing and sealing your windows can block unwanted airflow—although we will reiterate that the plastic shrink-wrap window kits won’t do you much good. 

But there’s more to the question: Does winterizing windows work?, and it’s founded in a bit of building science. 

Understanding the science goes back to the R-values we discussed above. The average R-value of a wall is about 12 to 19, while a double-pane window’s R-value clocks in at about 2—even for new windows.

That’s why the home performance industry uses this saying: Your worst wall is still better than your best window. 

Basically, that means even if you have an older wall with very little insulation, it’s going to perform better than any energy-efficient window could.

Why? Well, windows are designed to allow light and fresh air to pass through. So the simple truth is: The underlying problem with your drafty windows isn’t your windows at all.

That’s why lining your windows with plastic sheets (or even custom plexiglass inserts or thermal curtains) doesn’t do much to make your home more comfortable or help you save on energy bills. 

So what’s the real problem? A leaky thermal boundary.

Thermal boundary is a fancy term for your home’s barrier that keeps the outside out. It prevents “air exchange” so your home is warm and cozy in winter and fresh and cool in summer.

For a simple explanation of air exchange, watch this quick video:

So how do you stop unwanted air exchange around your windows? Glad you asked….

The fixes that resolve home comfort and energy waste issues for good

While windows are usually blamed for causing air exchange, remember that the real culprit isn’t actually your windows. It’s air leaks in your thermal boundary and insufficient insulation—especially in your attic.

When you seal these leaks through weatherization or air sealing and add more insulation to your house, you create a better, more powerful thermal boundary and a well-sealed building envelope that can permanently reduce the loss of indoor heated and cooled air. 

And these energy-efficient home improvements also reduce the intake of outdoor air through air leaks in your home, including around your windows.

Even if a DIY window insulation kit does work and is correctly installed, the effect is going to be minimal. So much so that in most circumstances, the plastic film would be almost imperceptible during a blower door test, which is the test used by home performance contractors to determine the amount of unwanted air exchange in your home.

So while the window insulation kit industry wants you to believe installing plastic film on your windows will help you save a ton on energy bills, the science just isn’t there.

To permanently fix drafts, uneven temperatures, and energy waste problems in your house, you’ll need to:

  1. Air seal your whole house, not just the windows.
  1. Upgrade your home’s insulation (especially in your attic), not just increase your home’s window insulation with plastic film.

Sealed did a great job with insulating my home. The drafts are gone which makes the house more comfortable and warmer. […] I’m saving money on my heating bill. Sealed did a great job and I highly recommend them.

John B., Sealed customer

Skip the plastic over windows. Get permanent fixes with a guarantee..

Even if you’re a fan of winterizing your windows with shrink-wrap (we know many homeowners who have used this method for years), that doesn’t solve the core issues that are causing your home to feel uncomfortable and waste energy.

(And these same core issues can also lead to ice dams, an inefficient HVAC system that needs to be replaced sooner than it should, and so much more. And those issues will continue long after you install window plastic all over your house.)

But at Sealed, we can help you fix these issues—including those drafty windows—once and for all. 

Love the house you’re in. Here’s how:

  1. We make your home energy upgrade process hassle-free—including flexible payment options and an energy-savings guarantee.
  2. We vet the best contractors in your area, and match you with the right one based on their expertise and the unique needs of your house.
  3. We meticulously research what rebates your project might be eligible for, even submitting rebate paperwork on your behalf.
  4. You get to sit back and enjoy a white-glove treatment that makes your house feel better year round without adding a layer of plastic to your windows.

Fill out our quick questionnaire to see if your home qualifies. (Trust us, it will take us less time to answer these questions than it does to unwrap the plastic cling-wrap of a window insulation kit.)

May 20, 2022