# Best way to cut rigid foam board?



## ponch37300

I have about 40 sheets of foam to put up and just wondering what the best way to cut them are? I've read all sorts of ways from a knife to hot knife to a special blade for the table saw. Just want to get whatever tool will make the job as easy as possible.


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## de-nagorg

A bread knife.

Anything with teeth will cause much dust of little granules of foam, that will stick to everything and be a #$%^&* to clean up.


ED


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## kwikfishron

I score and snap with a utility knife for the most part. I will use power saws too. I can't say that using a power saw makes any more of a mess than any other material being cut of the same thickness unless you're outside cutting on a windy day (no special blades needed).


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## gma2rjc

I bought a hot knife and tried cutting 2" foam board. Don't waste your money on it, it's extremely slow. IIRC, it cut at a rate of about 4"-5" per minute. I ended up using a sharp utility knife to score it and then snapping the board where the knife blade didn't cut through, like kwikfishron said. 

Buy extra blades because you'll need to change them frequently. When the blade isn't making clean cuts anymore, you'll know it needs to be changed.


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## de-nagorg

de-nagorg said:


> A bread knife.
> 
> Anything with teeth will cause much dust of little granules of foam, that will stick to everything and be a #$%^&* to clean up.
> 
> 
> ED


Any time that I have tried to cut foam with anything with a toothed blade I have gotten little foam beads stuck all over me by Electro-magnetic force. 

Maybe it's just my magnetic personality, but I doubt it. 


ED


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## asevereid

Extruded foam or expanded? 
With extruded I've found the best to be a simple 4" drywall taping knife. 
All you have to do is score up to an inch of depth, and then snap it. 

Sent from my Nexus 7 using Tapatalk


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## Fix'n it

use one of those snap blade cutters, the larger ones. extend the blade about 1"ish. then snap the foam. 
use a straight edge when cutting, i used a 4' level. makes things go much better.


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## Windows on Wash

Sharpen up a large putty knife.


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## Marty Gordon

ponch37300 said:


> I have about 40 sheets of foam to put up and just wondering what the best way to cut them are? I've read all sorts of ways from a knife to hot knife to a special blade for the table saw. Just want to get whatever tool will make the job as easy as possible.


 Without a doubt, you use an OLFA brand utility knife. YOu simply score and snap the board. YOu only need to cut about half way through and it will snap easily. You don't want to be "sawing" it with a serrated blade, that will create fragments, and also take forever.


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## bondra76

Windows on Wash said:


> Sharpen up a large putty knife.


genius


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## richard213

nice share


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## Bud9051

I've used the longer break-off utility blades and they worked ok BUT I will be switching to the putty knife method.

I would add to his video where he is cutting across 2 horses and the material is sagging in between. Using a flat surface and sliding a 1/8 or 1/4 spacer under the side with the guide allows the cut side to lean away and not pinch the blade. This has helped with my utility knife cuts and suspect it will help with the putty knife. Actually looks more like a 4" drywall knife.

Bud


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## Gary in WA

I agree, Bud. He even said it a was drywall "taping" knife in the video. Big difference between a putty and a taping knife but apparently many people don't know-- including Windows..  asevereid said it first- and no thank you's... go figure. Just don't use it for taping anymore as you will get sliced when cleaning it between interval applications, or cut the paper on the corner wall.

Gary


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## Windows on Wash

Thanks Gary. I am aware of what he said in the video. 

I use putty knife because the blade is a bit stiffer and I can get a better edge on it. Yes the steel is thicker, but when you are only cutting through 1" or 2" foam, it allows the blade to be stronger where you don't have an edge on it. 

I did see where asevereid had posted that but figured that a video might be helpful for some folks as a visual aid is helpful.


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## cloves

I have cut a ton of XPS and EPS foam. I cut long piece using my battery operated circular saw. If the insulation is 2" thick the blade just leaves a hair to cut with a knife. The battery saw is the way to go. Wear a dust mask if cutting EPS and of course its best to do this outside. EPS leaves a lot of dust, xps not so much.


With EPS a dewalt insulation knife and ruler is super easy.


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## carpdad

Just saw a bosch jigsaw knife blade. Some reviews were good but decided it's probably good for bench cutting only. If I was high on a wall trying to shape a panel, jigsaw may be too heavy. I am thinking of trying cordless bread knife, if there is such a thing. Also not sure how long a knife would hold the edge.


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## mikegp

de-nagorg said:


> Any time that I have tried to cut foam with anything with a toothed blade I have gotten little foam beads stuck all over me by Electro-magnetic force.
> 
> Maybe it's just my magnetic personality, but I doubt it.
> 
> 
> ED



I assume you're kidding, but if not, I think you mean static.


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## bondra76

I tried the putty knife trick - bought a cheap model ($2 or so) from Home Depot. Grinded it, and cut foam today. 

It took about 3 passes on 2 inch thick foam with the putty knife. Worked extremely well. I was pleased. I think the best thing in comparison to a utility knife is that the putty knife has such a long edge to it for thick boards that it really worked well.


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