How to Cut a Memory Foam Mattress

What Knife Can You Use to Cut a Memory Foam Mattress?

When it comes to memory foam, this material is quite pliant. Therefore, you won’t need to use any heavy-duty tools. A knife would do, but not just any regular knife. Here are the most common types you can use to cut a memory foam mattress:

• Electric knife. This one is probably the easiest to use. You won’t have to make much effort and can simply slide the knife through the foam. Plus, using an electric knife is the most likely to result in sharp, clean edges.
• Carving knife. A long, sharp carving knife is also a good option. With this knife type, you need to use short back and forth motions to cut through the foam.
• Craft (utility) knife. Such knives are typically sharp enough to deal with foam. Plus, they usually have a pointy tip that can make it easier to go through the material. However, in this case, you should avoid sawing motions. Instead, start with a shallow cut on a small section of foam and then make the cut gradually deeper until you reach the bottom and cut through the foam. Then, you can move on to the next section.
• Extra-large scissors. If you don’t have a suitable knife (or yours isn’t sharp enough), you can also use heavy-duty scissors. Cut smaller portions of foam and try to use only the tip of the scissors for a cleaner finish (and more precision).
• Long serrated bread knife. If it’s sharp enough, a bread knife can easily deal with memory foam. You will have to use sawing motions to cut through the material. The edges may end up a bit ragged, but that shouldn’t be an issue if you plan to encase your mattress into a fabric cover.

Other Tools You Will Need

So, if you have bought the best memory foam mattress and don’t want to say goodbye to it, a couple of simple tools can help you transform it into something new (like an RV mattress, for example). Here’s what you might need:

• a ruler or a measuring tape (to measure the needed dimensions);
• a sharpie (to mark the lines along which you are going to cut your foam mattress);
• a seam ripper (in case the mattress cover is not removable);
• a sewing kit (to tailor the mattress cover to the new dimensions);
• a drywall square or a piece of plywood/hardboard (to help you cut the mattress in a straight line and be more precise).

How to Cut a Memory Foam Mattress to the Desired Size

Now when you have all of your tools ready, you can start cutting your mattress. A quick word of warning before we begin, though: if you want to cut a memory foam mattress, you first need to check whether it contains fiberglass or not.  If it does and you start cutting, the fiberglass particles will be released into the room. And that can lead to very unpleasant consequences, to say the least (which may even affect your health) (1).

To find out whether your mattress contains fiberglass or not, read the description online or reach out to the company you have bought it from. If you learn that there’s fiberglass in your mattress, cutting it would not be an option. And perhaps in the future, you would like to consider one of the best memory foam mattresses without fiberglass. 

Also read: How to Pick the Best Mattress Without Memory Foam

And if your mattress is safe to cut, here are the steps you might want to follow:

• Take the mattress cover off. If it’s not removable, use the seam ripper to “open” your mattress up;
• Place your mattress on a firm surface. You can use a layer of plywood underneath to avoid damaging your floor in case your knife crushes into it. If the mattress is thin and relatively lightweight, you may want to secure it in place by putting something heavy on the corners (like a couple of books, for example). They don’t have to be extra-heavy (to avoid damaging the foam), just enough to prevent the mattress from sliding off.
• Determine the dimensions of the mattress that you want, measure it, mark the size, and draw the lines according to the new dimensions using a sharpie or a marker pen;
• Cut the mattress without compressing the foam. Keep in mind that the bottom section of the foam may be of a higher density, which means you might have to make a bit more effort when you reach it. Also, when dealing with softer foams, it’s better to use a drywall square (or a piece of plywood) to avoid warping the mattress.
• Trim off the excess bits if the foam edges turned out to be ragged. You can use a pair of scissors or a small knife;
• Cover your “new” mattress with fabric. That’s when that sewing kit may come in handy. If you don’t want to sew, you can also use safety pins. Simply tighten the cover against the mattress, fold the excess fabric, and pin it all together (but make sure you don’t puncture the foam).

How to Cut a Memory Foam Mattress Horizontally

In case you need to make your memory foam mattress thinner, you can cut it horizontally. Allow me to warn you right away: cutting a foam mattress horizontally can be quite difficult. It requires precision and, of course, special tools.

Now, you have a few options here. The most common one is a long horizontal saw. Ensure you hold the top section of the foam but don’t press on it too much while gently moving the saw through the material. It might be a good idea to put your mattress on a sheet or a towel as some foam bits may fly around in the process. The fabric underneath the mattress will catch them, making the cleaning process much easier for you.

Some users note that you can also use an electric saw if you have one. However, it might be dangerous, so I believe it’s better to stick to a regular one. When using an electric saw, you may get hurt, especially if you try to hold the top section of the mattress to prevent it from sliding off while you are cutting. A regular saw is much safer in this case.

Another option is a hot wire (if you manage to find a wide enough model for your mattress). Keep in mind that this method requires an extra steady hand. Also, it might be more convenient for you to cut the mattress if you place it on a taller base. 

That being said, I personally do not recommend cutting your mattress horizontally. It’s the easiest way to damage the foam. Plus, there’s no guarantee your “new” mattress will feel comfy enough. Instead, you might want to consider getting a new one. I’m sure you can find a perfect thickness option among the best memory foam mattresses according to Reddit users, for example.