I have started to make my own 1mm foam as it is either hard to source or too heavy or really expensive.
I used the old wire cutter method using a .3mm guitar string and a 12V transformer powered by a car battery.

I cut my foam by holding it in place with a sheet of glass. I use piano wire sticky taped just a little wider than the foam to a flat board to give me the varying height/thickness. All I do is slide the cutter along the wire until I get to the other side.
It curls from the heat:

I then flatten it again by sheeting it in between 2 pieces of glass and heating it in the oven at 145 celcius for 10 minutes - remove and let stand till cool. Then I remove it:

If you use 3mm foam, you end up with a 1mm sheet and a 1.5mm sheet!

Flat as a tack!

I curved this foam fuse around a balsa mold and then poured boiling water from the kettle on it to hold the shape better:

Here is the fuse. It's for my 12" Christen Eagle, same shape as the Micro Pitts - 2 grams AUW including formers.