I have a specialty end mill from Amana for doing foam. It's got a max RPM of only 6,000 so it requires a spindle to work. These end mills cut very cleanly and make a minimum of mess. For finish, I use an extra long ball nose. It seems that for foam, 1/2" end mills work best. If you're using a super dense foam, smaller end mills would probably work without tearout.
My take on foam is big end mills, low RPM's, faster speeds (6-8 IPS) yield a good quality cut.
Foam cutting generates a lot of static electricity so be aware of that.
ShopBot Details:
2013 PRS 96x60x12 (Centroid upgrade)
4hp Spindle
12" indexer
Aspire
Rhino
Fusion 360
Ferrari 360
Prusa MK3S+
Prusa XL multi-tool