Easy quick and effective.
Things you need
1. a wire coat hanger
2. A soldering gun
3. a hammer
4. a grinder of some sort.
Cut wire coat hanger long enough to replicate what you see in pic.
Bend the wire into the shape you see.
Now open the bend up enough so you can get at the part thats going to be cutting the foam.
Lay the wire on a hard surface, (preferably an anvil or block of steel) Pound this part of the wire flat.
Then use a grinder to remove more material from this area.
You want to make it thin enough that it heats up fast, but not so thin that it burns in half, or bends too easily.
close up your bend and attach to your soldering gun. Cut your foam.
I used it for several cuts and it works great. After a while the soldering gun body gets pretty warm so I would not use this for extended cutting times. but for 5 mins of cutting foam it does great.