I always just take the time to cut each one
with a razor knife with breakoff sections of the
blade & change the blade when it dulls.

some foam boards have a thin plastic overlay
on each side...this makes cutting problematic.
I usually take to plastic off before cutting.

best of luck

As above, I score it with a utility razor and snap it off against the edge of a sheet of ply or 2 by whatever. Or you can use a hand saw.

A Sawzall works great. Snap a line and cut. I'm cutting 4" and 5" foam this way.

I don't understand why your foam would gum up a tablesaw blade, but I'm cutting polyiso.

polyiso is easy to cut, it is the other foam board
with less R-value that is so difficult to cut.
as it is comprised of tiny styro balls formed to
make sheathing & topped on one side with
somewhat reflective plastic that quickly
dulls when left exposed.

these sheathing boards are difficult to cut.
little rigidity, and even with sharp razor knife
the particles fall apart as cuts are made,
having only one backing nothing holds it
together. IMO...real pita!

in my mind the high R-value(R-6-7 per inch)
is closed cell,the low (R-3 per inch) is open cell.
as mfg sheets do not define it this way...I hesitate
to do so online. but essentially tha is what it
is high density & low density foam.

just wondering OP, which type and how much
per sheathing? here 1" polystyrene is about
$20 each. no 2" unless special order.

best of luck op.

I forgot to mention that if you use the weed whacker on a windy day and the neighbors express concerns, just tell them that it's akin to vermiculite and will assist in water retention in the flower beds.

I bought seconds and paid only $5 for the equivalent of a 2x8. Each board is cracked so I have to square them and had to buy the pile. The boards are all 2 ft wide and very from 5ft to 7ft long. The boards are polystyrene I believe. They also had some 3" and 4" boards but I thought they would be even worse to cut. I may have cut too many on the first day. I cut about 30 boards in only 30 minutes and then I ran into problems. I used denature alcohol on the blade and was amazed how blue the rag became. Looking at the boards, the cuts were bright blue and very clean but the last few boards were much darker.

Thanks for all of the suggestions, I will try them this weekend.

Thanks

Fewer teeth is better than more (you want to cut down heating). Use a 16 or 20 tooth blade if you can find one. Get another cheap blade, cut till the first is gummy then change blades and drop the gummy one into undiluted simple green in the bottom of a five gallon bucket. It will be clean and ready to use by the time the second blade is gummy.