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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. 

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

So before you purchase a window insulation kit (or several) and cover your house in window plastic wrap, let’s dig in and take a closer look. 

Key takeaways in this homeowner guide:

  • Using plastic over windows as insulation doesn’t offer reliable protection against outdoor cold and heat.
  • Building science backs this up. And window kit manufacturers claim energy savings may be more dramatic that homeowners actually experience. Thermal curtains 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. (Learn how to get both at no upfront cost.)

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, you 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?

If you’re asking yourself do window insulation kits work?—as in, do the plastic sheeting insulation kits actually help insulate your windows and reduce drafts and energy waste—the short answer is no, not really.

But to understand why, let’s first discuss R-value. 

R-value is the measurement of thermal resistance of a material. R-value an important factor in insulating your home properly to increase your comfort, stop energy waste, and make the most of the HVAC system in your home. 

Let’s do a quick comparison:

  • A standard double-pane window’s approximate R-value is 2 (1).
  • The standard rolled-up batts of fiberglass insulation (like you might use to DIY your attic insulation) has an R-value of about 2 to 2.5 per inch. 
  • An insulated wall has an R-value between 12 to 19. 

But what about plastic window insulation kit sheeting? 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 plastic sheeting that comes in your window insulation kit is usually much thinner than that.

So even if you’re able to trap in minimal outside air behind the plastic, you won’t experience much additional insulation around your windows, even though these kits are marketed to people as window insulation. (We will talk about how to insulate windows from cold air or summer heat later in this guide.)

And while window companies or window insulation kit manufacturers might cite that sealing and insulating your windows alone can reduce anywhere from 30–50% in your energy bills, most homeowners won’t see that kind of dramatic reduction from putting plastic over windows—not even close. 

In fact, we believe these numbers are inflated or improperly understood. Most likely, they’re based on energy waste reduction numbers from completing whole house air sealing instead.

But don’t just take our word for it. EnergyStar.gov rates putting 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).

Whole house air sealing can reduce your energy use up to 30%, according to the U.S. Department of Energy (6). And those percentages increase 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% at zero upfront cost.)

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, either. 

Does putting plastic on windows help in the summer?

While window insulation kits are often advertised as a winter-weather fix, putting window 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. 

Read Do Thermal Curtains Work? to learn more about how they might be a good temporary fix for keeping summer heat or winter drafts out of your house.

How to improve window insulation

So if window insulation kits won’t work to significantly reduce drafty windows, what does work? 

Here are a few solutions for improving window insulation in the short-term:

  • Add thermal curtains and blinds. We mentioned this above, but thermal curtains can sometimes offer a better short-term solution for drafty windows than plastic wrap.
  • Install custom-fit window insulation panels. A custom-fit plexi-glass window insulation panel will provide you with a sturdy, reusable option that provides a tight seal (without all the tape and throw-away plastics).
  • Update your window weather-stripping. Over time, the weather-stripping around your windows and doors wears down. This is an affordable, easy fix to reduce window drafts. 
  • Reglaze your windows. If you have wooden window panes or windows with older glass panes, you may need to reglaze your windows. This is technical work, so make sure to get help if you need to.
  • Caulk air leaks around windows. Add a line of caulk to close open gaps and actively reduce unwanted airflow for good. But make sure you don’t block the weep holes, which are meant to be left open for moisture escape. 

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

How to insulate windows from cold

To insulate your windows against cold temperatures, adding thermal curtains and fresh weather-stripping 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.

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 weather-stripping. 

Solar window film is another add-on option that you adhere to the glass itself. It works as a temporary solution to block out UV rays and add a mild layer of heat protection.

Does winterizing windows work?

Winterizing your windows and sealing them can and does work at keeping out cold and hot air, depending on the tactics that you use. (Although we will reiterate that the plastic shrink-wrap window kits won’t do you much good). 

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

There’s a saying in the home performance industry when discussing uneven temperatures, energy waste, and insulation problems: 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 in creating an effective thermal boundary for your home than any double-glazed window could. (A thermal boundary is your home’s essential defense in keeping outside air out and inside air in.) 

This simple truth is easily illustrated in the R-values of these building materials that 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.

Here’s why covering up windows with plastic (or even custom plexiglass inserts or thermal curtains) doesn’t solve the underlying problem of drafty windows or a drafty house: Cost-effective windows aren’t intended to provide comfort or stop energy waste in your home; they are intended to light the home and provide fresh air on a nice mild day. 

A home without windows would be far more energy efficient, but no one would want to live there, right? 

And this is why window insulation kits don’t really work, as they don’t solve the underlying problem. 

In fact, the underlying problem of uneven temperatures and energy waste—and yes, even your drafty windows—isn’t your windows at all. 

It’s the exchange of air between the interior of your home and the outdoors.

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

Here’s how air exchange issues work—and how they can be fixed.

When indoor air escapes outside of your home through your attic (usually because your attic is insufficiently insulated), it creates a vacuum that must be filled. 

And at that point, your house sucks in outside air through gaps, cracks, and open seams in your home’s structure, also called air leaks, that are located around your windows, plumbing and light fixtures, doors, foundation, and more.

When you seal up 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 your windows.

So what’s the moral of this story? 

Even if you winterized all your windows with a DIY window insulation kit—or even if you completely replaced all your windows with brand-new ones—you still wouldn’t solve the underlying problem of air exchange that happens in every house that has insufficient insulation. 

(And guess what? Most houses have insufficient insulation, as insulation breaks down over time.)

And winterizing windows with short-term tactics—like window plastic—doesn’t even start to make a dent in that problem. 

Even if a DIY window insulation kit does work and is correctly installed, the effect it has 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.

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.
  2. Upgrade your home’s insulation (especially in your attic), not just increase your home’s window insulation.

Check out the 9 Signs of Energy Waste in Homes to discover if your home has energy waste problems (and learn what to do about them). 

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

Skip the plastic over windows. Get permanent fixes at no upfront cost.

We might be a bit biased, but we’re not fans of plastic window insulation kits. (Can you tell?) They’re a hassle to install, don’t have a real impact on drafts or energy waste, and only offer a temporary, short-term solution.

Even if you’re a fan of winterizing your windows with shrink wrap (we know many homeowners who have used this method for years), they don’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 once and for all. 

You get a house that feels better year-round, and we do all the work. We create a plan for custom energy efficient home improvements, manage the project, and stay accountable to the results—all at no upfront cost. (Yep, it’s true.) 

All the while, you’ll be stopping energy waste in its tracks.

Take our quick (and fun) quiz to see if your home qualifies. (Trust us, it will take us less time to complete this quiz than it does to unwrap the plastic cling-wrap of a window insulation kit.)

May 20, 2022