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Foam Board To Black Out Windows – Can It Be Done?

So, you’ve gotten that new window installed. This little project that you’ve been working on or meaning to get done for a while, so it feels good to finally finish it.

Foam Board To Black Out Windows

But, there’s a small problem. It’s winter, and for some reason, you can still feel a draft coming through that same window. It looks like whoever did that job may have left a small crack or exit hole for cold air to get in.

So, a handyman or the original window fitter is going to need to come back to fix it. But what do you do in the meantime, as that cold air still comes through?

This is one of the scenarios that many people are facing when they try to use foam boards to black out a window.

So, how exactly does this solution work? Why might you use this to black out or otherwise block windows in the first place? How do you do this? And, perhaps the biggest question is, does it even work?

Those are just some of the questions that we’ll be answering here. Foam board is an effective way of blocking out light and heat from a room with a faulty window. For the whys, the how, and the ifs, this guide has you covered!

Why You Might Use Foam Board To Black Out A Window

So, we outline a pretty good reason that you might want to black out a window with foam board. You don’t want any heat to be escaping, do you?

However, there are a few reasons why you might want to use this method for a window frame with issues.

Stopping Leakages

In the same way that a faulty window may not stop cold air from getting in and out of a window, the same is true for any wet weather that you might have outside.

Water can pretty much fit through any crack that it gets on, so if a cold breeze can get through uninterrupted, then water can too.

That extra moisture can cause mold to form in those cracks and crevices, so finding a way to block and black out the window is essential.

Room Too Hot

Cold air might be able to get into a window with a fault in it, but the same is true for the other extreme.

The glass in pretty much every window acts as a magnifying glass, which can cause serious issues with the temperature inside. A room can heat up to a temperature much higher than it is, even outside.

If the room that you’re in is housing animals or a child, then this can have disastrous health consequences for them, as they are especially at risk of overheating and passing out, or worse.

How To Fit Foam Board To Window

So, how exactly should you go about attacking foam board to a window?

Well, we should probably first go over some of the tools that you’ll need.

  • Hard foam board (make sure you have more than you think you’ll need).
  • Measuring tape
  • Razor blade
  • Duct tape

With those items covered, you can now follow these instructions.

  1. Measure the space for the window or window frame that you need to cover up. The foam board will need to fit into place, so make sure that you have a pretty exact measurement!
  2. Get your foam board, and mark out the right size. You can use duct tape to outline the border of the foam board.
  3. If you don’t have duct tape, a dark pencil or pen that stands out from the color of the foam will also work fine.
  4. Then, you can use the razor blade to cut the foam board down to the right size. If you’re unsure how much leeway to give yourself, always go further outside the border than inside. It will be easier to shave an oversized foam board down to size, than to bulk a too-small board up!
  5. Once you have made the cuts, simply snap off any excess pieces that hang over, then your board should be able to fit nicely and snugly into your window frame.

Other Tips & Helpful Advice

The Right Thickness

The thickness of the pieces of foam board that you’re using can have a pretty big effect on how successful it is at blacking out a window.

A thicker piece of foam board will not only be harder to budge or move from its spot, but it will also work much better as an insulation substitute.

Cold air can still get through thin pieces of foam, as can the magnified heat from the sun.


This is a step that many eager DIYers often forget. They’ll often put their foam board into place in the window frame, only to realize that it’s going to be incredibly awkward to take the foam board back out, because it has no handle.

At least, not without breaking it!

A small amount of rope and superglue is all it takes to make a rudimentary handle for your foam board, so you can then pull it out of the window frame slot.

Heck, if you still have duct tape handy, you can simply make a handle from a loop of this

There’s a good reason that duct tape is every home DIYer’s best friend, after all!

Is There Any Alternative To Foam Boarding Windows?

If you’re still waiting for a window repair expert to take a look at your window, what else can you do to stop a draft or overheating in your room?

This will depend mainly on what the exact problem is. If you know that the heat inside your room is escaping the window through the bottom of the frame, a long fabric door stop will stop the heat from escaping. Sometimes the most simple solutions are the best ones to use

Alternatively, you can also use plastic film if you want to use simple materials that you can find around the home. Simply spread the film across the affected area, apply heat, and the film should shrink.

Final Notes – How Well Does Foam Board Work?

So, with all that information covered, how well does foam board work for blacking out a window?

Well, as it turns out, it’s pretty solid. It will stop heat from leaving or entering the room, and water isn’t going to water around your frame and ruin it.

This isn’t a permanent solution to your window issue. But a foam board will serve you nicely in a pinch!

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