Insulating Windows and Doors from the Inside Out

Windows with closeable drapes.

Insulating your windows keeps both heat and cold out, while holding valuable conditioned air inside your home. And if your windows are old and drafty, you’ll need to do your utmost to keep them tightly sealed both summer and winter.

Below are tips on some easy ways to improve the insulation on older, single pane windows that can save energy and reduce your utilities during the heat of summer and cold of winter.

Install Window Insulation Film Kits

Plastic window insulation film is applied to the inside of windows to add an extra layer of protection between you and the elements. Make sure to install window film only on windows you don’t open very often, since once it’s installed the window can’t be opened to let fresh air in unless the film is removed.

You can find plastic film window insulation kits at most home centers and hardware stores. It’s best to apply window film in the early morning or late afternoon to prevent heat from the sun from distort the film.

Installing plastic film on window.

How to install plastic window film on windows:

  1. Wash the window.
  2. Stick the included double-sided adhesive tape around the window frame on all sides. Rub the backing tape smoothly and firmly to secure it to the window.
  3. Remove the backing, and take out the sheet of film (be very careful with the film as it will collect dirt and can be easily damaged).
  4. Stick the film carefully onto the adhesive, starting at the top and smoothing it down as you go (do about 6” at a time and go slowly) until the entire sheet of film is covering the window.
  5. Use a hairdryer to shrink the film and remove any wrinkles. Move the hairdryer in a pattern, and don’t hold it too long in one place, as it might cause the film to shrink unevenly.

Watch our video on How to Install Plastic Window Insulation Kits to find out more.

Caulk Around Windows

One of the best ways to improve the insulating quality of windows is to caulk any cracks and gaps around the windows both inside and out. You’ll probably need to caulk the joints again every few years to keep the seal tight.

Caulking around a window.

How to caulk around windows:

  1. Make sure to choose the right caulk. Ask which kind is best for your windows at your local hardware store. Use a quality exterior caulk when caulking outside and a paintable interior caulk inside.
  2. Use a scraper or putty knife to remove the old caulk before applying a new layer.
  3. Cut the end of the caulk tube at an angle, leaving a hole just smaller than the crack you’re sealing. Pierce the inside rubber seal with a wire hanger or other sharp object.
  4. Insert the caulk into a caulking gun, sung up the plunger, and press the trigger until caulk starts to come out of the tip.
  5. Hold the caulking gun against the joint at a 45° angle, and press the trigger while moving the tip smoothly along the joint. To avoid blobs, don’t stop moving the tip until the plunger has been released.
  6. After you’ve laid the bead of caulk, smooth it with your finger to fill any gaps and even out bubbles or blobs (this is called “tooling”).
  7. Let the caulk dry thoroughly before exposing it to water or painting over it. Some caulks can take up to 24 hours to dry.

Watch our video on How to Caulk Around Windows to find out more.

Closeable curtains on windows.

Drapes and Shades

Installing drapes, curtains, or shades on windows can improve the décor of any room. Keep them drawn during hot weather, especially on sunny windows, to help maintain a consistent temperature in the room.

Cellular Shades (often called “honeycomb shades) provide the most insulation for your home. They are designed so the layers of fabric form pockets of air when the shades are lowered, acting as an extra barrier between the inside and outside of your home. As an added bonus, cellular shades also help reduce noise from outside.

Draft snake on door threshold.

Draft Snakes

Draft Snakes are long sleeves of fabric filled with sand, rice, peas, or other grains which can be placed in front of entry door thresholds to stop drafts.

You can buy premade draft snakes or make your own. Either way, you can find colors and patterns that fit your personality and the look of the room. Read our article on How to Make a Draft Snake to learn how.

Improving the insulation around the windows and doors in your house doesn’t have to be expensive or difficult. But the better insulated they are, the lower your heating and cooling bills will be.

Regardless of whether your budget includes replacing your windows and doors or improving the ones you have, it’s important to keep your home as tight and well sealed as possible both winter and summer.

About the Author

Melanie Hargrave enjoys tackling home improvement projects, and she recommends PNR Screens in Victoria, BC, for all your window needs.


  1. Would interior storm windows be a better system to use than using window films every year? Could you give me suggesting in which direction to go.


  2. We had Window World replace all of out windows except the square bathroom decorative window. We plan to do bathroom window next. We love our new windows!

  3. You can also use removable caulk on the inside of windows, where the sash meets the window frame and where the two sashes meet, assuming you have sash windows. It helps keep the cold drafts out. You can just peel the caulk off in the Spring.

  4. Five years ago, I had new double pane windows installed. Both parts tilt in so I can clean them. This year, along the side edges where the 2 parts come together has an air leak. From your website, you may call them sashes?? The windows already have double locks. The air is coming from the area where the windows slide up and down. How to do I correct this. I could not locate the answer on the web. This is my first home and your tv show, website, etc has been a tremendous blessing to me.

    • Glad you enjoyed this article, Cindy! Homes regularly expand and contract, so it’s definitely good to insulate those windows and doors regularly.


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