Cutting Foam Rubber

Any suggestions on cutting foam rubber cleanly and not hacked with an exacto. I have sheets of 1/4" that I want to glue together to make 3/4" thick. I then need to carve it for prototyping to resemble a molded/die cut part. The size of the part is about 2x3" so fairly small.

Thanks for any suggestions.

I have heard but never tried, saturating with water, freezing, and shaping the frozen block.

See if you can find an electric kitchen knife somewhere. The counter moving blades are really good with soft, squishy stuff.

Why foam rubber? Is it a functional mold, or just for looks? Instead of laminating different layers of rubber, maybe look at lino pads. They are meant to be carved for printing. Or something easier to carve like wood or MDF and go at it with a dremel. Or consider doing making a prototype of the object as a positive and then casting a silicone mold around it if you need to make multiples.

Approach all depends on what you are trying to achieve.


The size of the part is about 2x3" so fairly small.

Yeah, 2" x 3" is fairly small…

small enough that if you make a masonite (aluminum or steel would be better) template you can use it compress the foam and cleanly cut it with an X-acto. Compressing the material is the trick. :wink:

How intricate is the “interior” of the part?

Agreed, compressing foam is how to get a clean cut, that’s what I have done. Now wetting and freezing I never heard of that, but maybe try that too on a small piece.

Thanks for all the suggestions. I actually did end up soaking and freezing the foam, I then cut out a profile of the shape I wanted with wood, and then used thin sheet metal and wrapped that around the profile edge of the wood… I then sharped the bottom edge. I used this as a sort of die cutter, which actually worked really well. Unfortunately, it is only good for one cut because the edge gets warped/bent when it cuts through the foam and hits the work surface.

I did also make a fixture to compress the foam and try and cut it with a profile guide. The edges were still to jagged. I used a box cutter, hook blade, serrated blade, and exacto blades with no luck.

Has anyone tried using a hot knife (see link below)? I think this is more for foam, rather then rubber foam. So before i run out and spend 70-100 bucks on something ill rarely use I wanted to see what the core community had to say.

P.S. to clarify on the project, this is a prototype that must be functional to securely hold an electronic consumer good. I thought about making a mold since my design has complex surfaces, however I didn’t know of any rubbery foam that I could pour into a mold.

Thanks for any more suggestions!

For accuracy and finish, I’d make a CNC or RP part, then cast it using silicone or PU foam, or even some sort of construction foam or caulking might work.



Has anyone used this stuff before… LAST-A-FOAM® FR-4300. If I am reading it correctly from General Plastics website. It is apparently is a heat moldable foam? I haven’t been able to find much info about it. if you have used it please let me know about your experience. I dont even know where to buy it.

Interesting material.

Structural foam means hard foam. It reminds me however that soft EVA foam can be easily heated and formed, you might be able to build prototypes of certain shapes that way. The same way foam is molded in factories. Heat it up in a convection oven, around 200-225 degrees F, not close to the heating elements, and form it or compress it into the shape you are looking for. Sheets or blocks of EVA foam are easy to find, even in the pool toy section at local store. Cuts nice also.

Hey great thanks for the tip nxakt… I’ll give that a go. To Rkuchinski, I did use a foam calking in a sort of mold. That did work pretty well, just didn’t give me the right rubberish foam feel i needed to securely hold my electronic device. It ended up being more of a hard coating over styrofoam. I might try coating it with a different surface to see if that helps.

Thanks for the help everyone.