How to Insulate Windows

By Julie Thompson | Advertiser Disclosure

The energy lost through windows is responsible for 25%–30% of heating and cooling energy use. Not only can insulating your windows save energy, it can lower your heating bills and make the indoor temperature more comfortable.

When to insulate your windows

The best time to insulate your windows is in the fall before the temperature drops. Since it may be difficult to assess how insulated your windows are when the indoor and outdoor temperatures are relatively the same, wait until it’s time to start using your heater, as the contrast between indoor and outdoor temperatures is greatest at this time.

If you’re not sure if your windows are already insulated, here are some signs that can help you tell if you need window insulation:

  • You feel a draft coming through one of your windows. Insulated windows will keep warm air in and cold air out.
  • Look for condensation trapped between panes of glass, usually along the edges. This is an indication that the window frame is deteriorating and that the glass may be compromised in the form or a hole or crack.
  • A smoke test is another effective way to test your windows. Use a candle and trace the window frame at a close but safe distance. If the smoke starts to go toward the window at any point (instead of the smoke pointing straight up), there’s a leak present.
  • Your energy bills are higher than normal.

Windows that have recently been installed should not need insulation. If you feel a draft from these windows, the window is either defective or installed improperly. Check to see if your windows are covered by a warranty before starting any insulation work.

How to insulate windows

Once you’ve determined which windows need insulation, you’ll need to decide which method you want to use.


  • Tape measure
  • Scissors
  • Window cleaner
  • Paper towels
  • Utility knife
  • Caulking or expanding foam gun
  • Putty knife

Caulk your windows

If you have small holes or gaps in your windows, caulking them is the easiest form of window insulation.

Rope caulk

Rope caulk comes packaged in a roll. This type of caulk is made from a putty that fills the drafty seams in your windows and prevents air from coming in.

  1. Cut the caulk into strips with a putty knife to match the length or your window seam.
  2. Use your fingers to press the putty into the seams until you no longer feel a draft.
  3. If you need to remove the rope caulk, use your fingers or a putty knife to gently lift the caulk from its position. Check in on the condition of the rope caulk periodically to make sure it’s still effective.

Exterior-grade caulk

You can also use exterior-grade caulk to seal your exterior window frame. Perform this task on a dry, sunny day to avoid getting water in the caulk. Note: caulk can break down from the sun and elements, so it will eventually need to be replaced.

  1. Scrape any old caulk or peeling paint with a putty knife and remove it from around the window frame. 
  2. Apply the caulk around the window frame with a no-drip caulking gun at a 45-degree angle so that all cracks are sealed.
  3. Let the caulk properly cure for 24 hours.

Add weather stripping

Weather stripping is one of the safest and most cost-efficient ways to prepare your home for cooler weather. Not to mention, it can reduce noise transfer and help lower your energy bills. Self-adhesive weather stripping can be purchased at your local home improvement store.

  1. Clean the area with a homemade window cleaner and dry the area before applying the weather stripping.
  2. Use a measuring tape to determine the dimensions of your window.
  3. Trim the weather stripping to match the window dimensions.
  4. Remove the backing of the weather stripping and stick to the inner frame of your window. It should fit as flush and snugly as possible.

Note: Weatherstripping can last for one to three years.

Insert spray foam

To seal the exterior frame of your window, you can use low-expansion spray foam.

  1. Spray the foam in one of the window’s corners. Take note of the amount and force that you applied the foam with.
  2. Wait the recommended time (found on the product) for the foam to stop expanding.
  3. After the time is up, observe the window corner. There should be minimal foam without excess expansion.
  4. Continue applying the spray foam around the entire window frame, even if the draft is only in one spot. This will insulate the entire window and prevent any cold air from leaking in.

Use draft stoppers

Draft stopper kits can be purchased from home improvement stores and online. They are made to be placed on a bottom windowsill or at the bottom of doors that lead to the outside. Note: you might need to add other forms of window insulation if more drafts are present.

  1. Cut the foam core to the width of your window.
  2. Insert the foam into a washable fabric cover.
  3. Wedge the stopper at the bottom of the window.

If you don’t want to buy a draft stopper, you can make one with materials found in your home.

  1. Use heavy fabrics, like an old pair of jeans or a blanket. 
  2. Sew the draft stopper and fill it with dry rice to make it easier to move around, or simply roll your fabric until it forms a thick enough cylinder to cover the window or door draft.

Additional window insulation techniques

Energy-efficient window treatments

Window treatments are an effective insulating tool. They’re also pleasing to the eye and can be changed with the season or your design style. Energy-efficient window treatments are available in blinds, drapes, shades, and shutters.

Blinds and drapes

Blinds and drapes provide a barrier against cold air leaking in. Made from heavier materials, their variety of design choices make them a great addition to shades and shutters. For drapes to be the most effective, make sure they extend past the entire frame of the window.


Popular shades for window insulation are double-cell cellular shades, Roman shades, and solar shades. All of these options can increase energy efficiency in your home. Solar shades are a great insulation option for summer or for those who live in warmer climates. They allow you to see outside while blocking harmful UV rays.


Shutters are installed directly to the window frame, creating a tight seal. You can easily block unwanted cold or hot air and control how much sunlight you let in with this option.

Window insulation panels

Aluminum frame window insulation panels have self-adhesive weather stripping around the entire frame. They seal your existing window by creating an air pocket that traps air leaking into your home.

The panel will only work if it’s sized correctly to your window, so be sure to measure your window for the correct dimensions before purchasing a panel.

Although window insulation panels can keep drafts out, the solution is temporary. You’ll need to remove them to open your windows, so be prepared to install and remove them every year.

Window insulation kits

Window insulation kits are relatively inexpensive and include clear window insulation film and double-sided tape. You’ll need to seal the film with a hair dryer to complete the task (a hair dryer isn’t included in the kit).

  1. Begin by trimming the clear film to the inside dimensions of your window.
  2. Add the double-sided tape to the inside frame.
  3. To increase efficiency, apply a second layer of double-sided tape next to the one you’ve already placed. 
  4. Cut strips of bubble wrap to fit the window and attach them to the inner layer of double-sided tape. Keep in mind the bubble wrap window insulation will obstruct your view to the outside so only apply this material to non-essential windows.
  5. Attach the clear insulation film to the tape and use a hair dryer to stretch the film tight. The film should not be touching the window and should feel like an air pocket when lightly touched.

3M Indoor Window Insulation Kit

This kit includes easy-to-apply film sheet and two rolls of tape. It has the capacity to insulate five 3’x5′ windows. Not only does this insulation kit lower heating costs and save you money on your monthly energy bills, it increases the R-value of a single-pane window by 90 percent.

Magnetic window insulation

If you need to occasionally open your insulated windows, you should consider removable magnetic window insulation. Unlike other window kits that use seal tape, this application uses magnets.

  1. To install the magnetic window insulation kit, you’ll need to first paint the inside trim of your window with several coats of magnetic paint. Magnetic paint can generally be found in the paint aisle at home improvement and department stores.
  2. Once your magnetic paint is completely dry, cut the vinyl to fit your window.
  3. Apply magnetic tape to the perimeter of one side of the vinyl, then attach this to your window trim. The magnets in the tape will keep the insulation in place.

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