Memory Foam Cutting Technique (9-Step Guide)

Mattresses and mattress toppers made of memory foam have become the go-to solution for people seeking a more conforming material to sleep on that molds well to the body.

You may have bought a larger size memory foam mattress initially. But plans changed and now you intend to cut the memory foam to size.

Perhaps from a king in one bedroom to a queen in another. Or, cut it down in half to make two mattresses for the kids.

Cutting a memory foam mattress or topper to size requires the proper technique so you don’t end up with inaccurate sizes and uneven edges.

The following are things you need to know before proceeding.

Warranty vs. Guarantee

Mattress warranties are different than comfort guarantees. Although your manufacturer or retailer may have a liberal comfort guarantee, warranties are generally quite limited and restricted.

Warranties are typically limited to manufacturing defects. Any abuse of the mattress will void the warranty.

In the eyes of the manufacturer, a stain on the cover will void the warranty. You could imagine how aghast they would be should you claim a warranty on a mattress to which you altered the size.

Taking a knife to your mattress voids the warranty.

How to Cut a Memory Foam?

It’s for your RV or boat or custom bunk bed – you have a reason. The mattress will be cut.

It is just a question of how to do it. This will take the proper tools and techniques.

Tools for the Trade

In order to cut the foam, you need:

  • Craft utility knife. Sharp, long thin blade. Not a box cutter.
  • Carving knife. Serrated.
  • Electric carving knife. It’s not just for turkeys anymore.
  • Shears/Scissors. Long. Can be used with mattress toppers.
  • T-square, Straight Edge. Long.
  • Chalk line marker.

Cutting Technique

Following this step-by-step instruction should give you a nice, clean cut for your memory foam mattress, gel memory foam, or mattress topper:

Step 1:

Expose the foam. Time for your mattress to get naked. Check for zippers in the cover or find a seam in the cover. Carefully remove any cloth, vinyl coverings.

Step 2:

Examine the exposed mattress. Are all the layers bonded together? If not, you may have to cut a topper layer separate from the base layer.

Step 3:

“Measure twice, cut once.” You only get one chance, so make it count.

Step 4:

Mark your line. Use a T-square or straight edge to lay your guideline. Snapping a chalk line could also work.

Step 5:

Stage your work area. Will you be cutting off an end, slicing a few inches off the side, or splitting your mattress in half? You need your cutting implement to reach through the mattress.

As the mattress is cut you must manage the discarded piece so that the cut remains straight and clean.

You may need to rig a space with plywood and cinder blocks that will support each portion of the mattress while allowing a cutting channel.

Step 6:

If you use a utility knife, use shallow long cuts. Slice but do not saw. Work your way along your lead line slicing progressively deeper similar to fileting a large salmon.

Step 7:

If you use a standard carving knife, you will need to use a cutting motion up and down. Do not force the knife on the mattress faster than the cutting opens up the mattress.

You want a smooth, straight cut.

Step 8:

If you use an electric knife, it will provide the up and down cutting motion. You will draw the knife down the cut line as the knife does the work.

This will move more quickly than the manual knives so that you must take care to not let the cut stray from the marked guideline.

Step 9:

Shears or scissors would only be used for a thinner mattress topper.

Rather than long lopping cuts, use short cuts towards the hilt of your tool. This is where the greatest cutting power is achieved.

Post-cut Considerations

Well, now you’ve done it. You have a freshly cut, custom memory foam mattress. Are you done? Not quite.

  • You will want a mattress cover to protect your mattress. If you are crafty and have a sewing machine, have at it. If not, contact a local upholsterer. They have the machines and skills to cover your mattress. Or, check the internet. There are vendors online who will create a custom mattress cover.
  • Bedding. It is unlikely you can find a fitted sheet for your new mattress, but you can make it ‘old school’ with two standard sheets. Now, you may have a lot of excess sheets. You or a seamstress can cut down and seam standard sheets to fit your new mattress.
  • Clean your tools. Best to give those knives a good wash before you carve the bird or slice the French bread.
  • If you have the storage space, save the excess foam. It may be just the thing for some cushions, a pillow, or some craft project.


If you have all the means discussed, a sharp electric knife will provide the best, most uniform cut. Be sure to set a good base for your work.

As a reminder – your warranty is voided as soon as you take any tool to your mattress.

Similar Posts