Best way to cut foil-backed Expanded polystyrene?

[MrBreeze]

While a hot knife might be the least messy for standard polystyrene, not sure it would work with the foil? (not to mention the off-gasses may be slightly toxic)

A saw - hand, power or table would make short work of it, but the mess!

A utility knife, scoring and snapping like drywall?

Something else?

 

[PugetDude]

While a hot knife might be the least messy for standard polystyrene, not sure it would work with the foil? (not to mention the off-gasses may be slightly toxic)

A saw - hand, power or table would make short work of it, but the mess!

A utility knife, scoring and snapping like drywall?

Something else?

Vaughn Bear Saw- ultra thin kerf.

 

[The Cobbler]

I would think a utility knife would do the trick .

 

[PhysicsDude]

I use a utility knife. It doesn't go all the way through with 1 cut, I score it deep, then spread the cut, and do another cut with the knife all the way through.

No need to make a mess with any sort of saw.

 

[6PTsocket]

While a hot knife might be the least messy for standard polystyrene, not sure it would work with the foil? (not to mention the off-gasses may be slightly toxic)

A saw - hand, power or table would make short work of it, but the mess!

A utility knife, scoring and snapping like drywall?

Something else?

I cut thick soft foam with knife blade on a jig saw. I know there are long versions and even double blade ones that work like an electric steak knife. If it will cut the foil there should be minimal mess. I have not tried it for what you have but that is what I would try first. HEY, it just occured to me; try a serrated electric steak knife.

Sent from my SM-G900V using Tapatalk

 

[matt_i]

I use a utility knife. It doesn't go all the way through with 1 cut, I score it deep, then spread the cut, and do another cut with the knife all the way through.

No need to make a mess with any sort of saw.

This is basically my technique. Its critical to have a very sharp blade, either one you got out of a package or one you personally touched up the edge with a stone or diamond file. One that hacked up 12 cardboard boxes isn't the right tool as it skips and tears instead of cleanly cutting. I mark a line with a sharpie with a drywall square or a long steel flat bar, then hand score about 1/4" deep. Then go back and score the entire depth of the blade, which isn't enough for 1" thick material. But it will crack like drywall at that point, and then you can flip it and easily slice the opposite skin.









I got a lot of practice double-wrapping this duct on the cold side of my attic

 

[rlitman]

What he said about a sharp knife, score and snap. Just one note. Most polyiso board I do this to has a thin layer of fiberglass mesh in the middle. Not sure if your board does, but it really dulls the knives fast.

 

[stm317]

If you're going to be doing lots of similar cuts, I'd use a table saw with a fence. It will be messy, but it makes clean cuts that are easily repeatable, and does it in a timely manner. I rented one locally and used it to rip 36 sheets down to various measurements. I value my time, and I was able to make all the cuts I needed in a few hours of work. Had my 32X48 building insulated between girts in a weekend all by myself. It would've taken me several weekends if doing it all by hand. If you go this route, breathing protection and eye protection are strongly suggested. That dust can be nasty.

If you're doing smaller quantities, or more detailed work then a sharp box knife works well. I like Matt's technique.

 

[Donald Cook]

I cut some 2" with an old very sharp bread knife, I used WD40 to keep it from binding, It worked good for me, and very little mess.

 

[NUTTSGT]

The utility knife works good with polyiso, but the OP is asking about polystyrene. Utility knives generally don't work that great on them and usually they are thicker than what the blade is deep.

I have an old serrated steak knife that I use to cut polystyrene, with or without foil.

 

[kj_mustang]

Use a narrow putty knife with one long edge sharpened, works great on 2" XPS.

 

[Jon_E]

I use those box knives with the snap-off, replaceable blades. They work great up to about 2" thick material. I've been cutting polyiso with mine, fiberglass facing both sides of the sheet. Change blades often. Score and snap the sheet, works pretty well too. A table saw would make a horrible mess.

 

[strutaeng]

I use those long snap-off knifes to cut right though:

https://www.homedepot.com/p/DEWALT-25-mm-Metal-Body-Snap-Off-Knife-DWHT10045/202710467

Very easy for XPS.

I installed 2 layers of 3" polyiso with the fiberglass facing on my house roof and bought an Milwaukee "insulation" knife, but didn't work well. I used the snap-off blade, but it was a challenge. I've seen commercial roofs cutting polyiso with drywall jab saws, but does create a mess. They have a leaf blower for this.

1" XPS is easy to cut.

 

[csp]

Just installed 20 sheets of XPS and used my Dewalt snap off blade for the cuts. I have a hot knife and gave it a try, but it's just not as fast and score, snap, cut or as accurate due to the thickness of the hot blade. The foil is plastic based, so it does melt.

 

[ishiboo]

Utility knife is the only sensible way. No need to make a mess.

 

[hand]

I use those long snap-off knifes to cut right though:

https://www.homedepot.com/p/DEWALT-25-mm-Metal-Body-Snap-Off-Knife-DWHT10045/202710467

Very easy for XPS.

I installed 2 layers of 3" polyiso with the fiberglass facing on my house roof and bought an Milwaukee "insulation" knife, but didn't work well. I used the snap-off blade, but it was a challenge. I've seen commercial roofs cutting polyiso with drywall jab saws, but does create a mess. They have a leaf blower for this.

1" XPS is easy to cut.

+1 for the long snap off blades. I used with 2" Thermax (heavy foil faced) to good effect - simply hold a straight edge in place and run the blade from end to end of the sheet.

Definitely worth a couple extra dollars for a quality metal handle for the blades vs. the cheap plastic. I can't imagine a saw being easier or cleaner.

 

[Falcon67]

Like what matt_i used - score with a utility knife using a big T square and snap. No need to cut through.

 

[SmartShoe]

Use a narrow putty knife with one long edge sharpened, works great on 2" XPS.

This is what I did when I installed baffles using blue board in the room over my garage. The sharpened edge of a putty knife was so much smoother and easier than using a utility knife.

 

[aczr2k]

Table saw works wonderful.

 

[Stuart in MN]

Serrated bread knife?

 

[Markfothebeast]

Like what matt_i used - score with a utility knife using a big T square and snap. No need to cut through.

Agreed. Use a NEW razor and cut it at the proper angle without forcing it too hard..

-Markfothebeast-
(www.youtube.com/markfothebeast)

 

[Orangestang]

Agreed. Use a NEW razor and cut it at the proper angle without forcing it too hard..

-Markfothebeast-
(www.youtube.com/markfothebeast)

I used a circular saw kind of messy but it works, scoring it won't work the foam I used wouldn't score and snap.

Sent from my Pixel using Tapatalk

 

[gnpenning]

I don't know what size you are cutting too. Our local Insulation house sells 24" wide the same price per foot as 4' width. No cutting needed for my project. Plus they are much cheaper than the box stores.

When I do need to cut I treat it like drywall, square and utility knife.

 

[MrBreeze]

1.5" thick EPS
https://www.lowes.com/pd/Common-1-5...ded-Polystyrene-Foam-Board-Insulation/3362408

Doesn't score/snap as Polyisocyanurate does.

 

[Nivekdodge]

Find a way to mount the knife on the table saw so you can use the fence. But of course be careful

 

[MrBreeze]

Going to give this a try:

https://www.homedepot.com/p/Bullet-Tools-7-25-in-CenterFire-Foam-Cutting-Blade-CC52-1507/205754774

http://www.bullettools.com/insulation/

 

[Crazyjake8493]

I use a table saw for long straight cuts and an old bread knife for knotches and holes. A circular saw, jig saw, or band saw work well too.

 

[DaveOmak]

I watched a u-tube video where a guy sharpened the edge of a putty knife.. I tried it and it really cut blue foam board easily and straight... I had to polish the body of the knife to get it to draw easily but it worked... Note the right edge of the blade...

 

[turbodave]

I did the ceiling of my garage with these boards and the best knife I found for it was a ginsu steak-knife from one of those 10 for $1 sets.

 

[EdT]

I've cut a lot of polyiso foam with a table saw. If you use anything that makes dust be aware that the dust from plastic does not soften up in water (tears) like wood dust does,so if you get in in your eye, it scratches 'til you rinse it out. I learned this the hard way.

 

[Markfothebeast]

Find a way to mount the knife on the table saw so you can use the fence. But of course be careful

I built a "jig" type deal with 2x4s in the vertical position. So when i'd slide the sheets through, there'd be 2 blades to score them. Worked slick.

-Markfothebeast-
(www.youtube.com/markfothebeast)

 

[jgorm]

Other long snap off long blade user here. Everything else makes a horrible mess.

 

[jdieter]

Agree with the post above about sharpening a putty knife on one edge and a straight edge. Works much better than a utility knife, clean deep cut as deep as the knife once it is sharpened and polished. Just did 2000 sq.ft. of rigid Styrofoam and method worked great.

 

[Crazyjake8493]

I've cut a lot of polyiso foam with a table saw. If you use anything that makes dust be aware that the dust from plastic does not soften up in water (tears) like wood dust does,so if you get in in your eye, it scratches 'til you rinse it out. I learned this the hard way.

Yeah I forgot to mention this. Always use dust collection if cutting foam with a table saw. Still makes a bit of a mess, but it's a clean straight cut every time.

 

[MrBreeze]

There's a big difference between Polyisocyanurate ("RMax") or Extruded Polystyrene (XPS - the pink brand stuff) vs EPS (Expanded Polystyrene)

EPS doesn't "score 'n snap" like the others.

 

[8mpg]

Table saw works wonderful.

I agree...table saw/circular saw

 

[NUTTSGT]

There's a big difference between Polyisocyanurate ("RMax") or Extruded Polystyrene (XPS - the pink brand stuff) vs EPS (Expanded Polystyrene)

EPS doesn't "score 'n snap" like the others.

Yep.

Like I already mentioned, I use a steak knife. . . . I remember Mom opening the box to the set when her and my dad were still married about 40-some years ago. I've cut a bunch of polystyrene with it, enough that the tip has wore off from cutting on concrete.

 

[SmartShoe]

I have used a table saw to cut foam board as well as a sharpened putty knife. Each method has its place. On the table saw I took an old, crappy blade and turned it around backwards. It zipped through the foam board like a hot knife through butter.

 

[jkeyser14]

If you just score both faces using a utility knife it snaps just like drywall. Even on thick 2" sheets.

 

[MrBreeze]

Going to give this a try:

https://www.homedepot.com/p/Bullet-Tools-7-25-in-CenterFire-Foam-Cutting-Blade-CC52-1507/205754774

http://www.bullettools.com/insulation/

SUCCESS!!!!!

I used the 7.25" blade in my 18V Milwaukee circular saw and it cut like butter with VERY LITTLE mess.

BTW, I have no affiliation with the maker of this product.

Note, there's a big difference between Polyisocyanurate ("RMax") or Extruded Polystyrene (XPS - the pink brand stuff) vs EPS (Expanded Polystyrene)

EPS doesn't "score 'n snap" like the others, but this blade worked amazingly well on EPS.