6 DIY Ways to Insulate Windows

Adding Insulation Film to a Window
Shrink-wrap style insulation film is a popular way to insulate poorly performing windows. BanksPhotos/Getty Images

When extreme cold or hot temperatures bear down, your home's interior may suffer if the structure's thermal envelope isn't properly doing its job. Cold and heat can enter your home through a myriad of avenues. But before you look at the walls, ceiling, and flooring, consider those intrusion points that are the more likely culprits: windows. Extreme temperatures can press into your home both through and around windows, even with quality windows that are in good shape.

Adding window insulation, a simple and inexpensive project, can reap huge benefits for your comfort level and for your monthly energy bill.

Why You Should Insulate Your Windows

Every window, old or new, good or poor, can benefit from additional insulation. While insulation cannot transform a bad window into a high performance window, it can make a marginal difference to get you through a season or two. Newer, top-quality windows may not require the whole array of insulating techniques, but they too can benefit from an additional measure, such as the installation of insulating draperies or cellular blinds.

When to Insulate Your Windows

Ideally, you should insulate your windows before cold weather sets in. Yet, because it is difficult to assess the state of windows' insulating abilities when temperatures inside and outside are nearly equal, you may wish to wait until it is time to start cycling on the heat or air conditioner.

This contrast between inside and outside temperatures will be greater at this time. Also, if you choose to use a thermal imaging camera, the camera will register heat or cold loss patterns better at this time.


The cost of insulating windows should not be an obstacle, since most methods are inexpensive.

Shrink-fit window film insulation, caulking, weatherstripping, and spray foam are so cheap that you can recoup their costs in energy savings. Draft stoppers can be made from old fabric and are practically free. Of all of the methods, energy efficient window treatments are the most expensive, costing up to 25% more than the ordinary, non-thermal versions.

Window Film Insulation

Transparent window film comes in large sections that are cut to window size. The film attaches to the window frame with double-sided tape. Lightly blowing warm air over the film with a hair dryer causes the film to tighten. Acting much like the argon or krypton gas that fills the space between double-glazed window panes, the dead air pocket created between the film and the window hinders air infiltration. Window film insulation is different from reflective window film (or low emissivity film) which sticks directly on the glass.


Window film has been proven in university laboratory tests to lower a window's u-value by up to thirteen percent (lower u-values mean greater energy efficiency).


Upon removal, the double-sided tape may strip off paint from your window frame.


When you have cracks in the window sash or around the window that are 1/4 inch wide or less, apply paintable water-based latex caulk.

Use silicone-based caulk for metal and glass surfaces.


The only way to fill thin cracks, caulk is inexpensive and easy to apply.


Caulking can be unsightly if left unpainted. Silicone caulking cannot be painted. All caulking periodically needs to be reapplied, especially if the window area is subject to expanding and contracting.


Stationary parts in or around windows can be filled with EPDM, foam, or felt weatherstripping. Movable parts of the window, such as the gap between the sash and the window frame, also can be filled with weatherstripping on a temporary basis.


Unroll the weatherstripping and force it into place with your fingers: it's that easy. Weatherstripping is simple to apply and will leave no residue or mess when removed.


When applied to movable window parts, the window cannot be opened or closed.

If you do wish to open the window, the stripping must be removed, then applied once again.

Spray Foam

Large, accessible gaps around the window frame should be filled with polyurethane, expandable spray foam. Insulate with spray foam only if you already have access in the form of large holes or cracks. Stripping away drywall and plaster to gain access can only create more problems.


Aided by a long nozzle, spray foam can reach areas that you cannot reach by inserting fiberglass insulation by hand.


Rarely will you have enough access to the wall cavities around the window. Also, spray foam is difficult to control and can expand out of the wall cavity, onto the wall or floor.

Energy Efficient Window Treatments (Thermal Curtains)

Window treatments that provide extra insulation tend to come in two forms: thick side-drawn draperies or vertically-drawn pleated (or cellular) blinds. The draperies are far thicker than ordinary ones and have tie-backs to hold them against the wall, further blocking air infiltration. Pleated blinds that move up and down look like typical mini-blinds at first glance. Yet extended, their cellular construction forms air pockets that help maintain inside temperatures.


Recommended by the U.S. Department of Energy, research has shown that insulating window treatments are highly effective at controlling inside temperatures. During hot months, draperies with white plastic backings can bring down the home's heat gain by one-third. 


Insulating draperies and blinds only work when closed. Pleated blinds do little to control air infiltration, as they are too light to prevent air from moving into your home (much heavier, draperies do a better job at this).

Draft Stoppers

Often used to block the gaps under doors, fabric draft stoppers, or snakes, can also block the gap between the bottom of the window sash and the window frame.


You can make your own draft stopper from long socks or sewn from fabric. Rice, popcorn, or dried beans are used to fill the snake.



Draft snakes have few downsides, as long as you understand that they block only one of four potential draft points along the perimeter of a window sash.