PUR foam like Cellotex/Kingspan, main hassle is the dust , extraction helps but it sticks to things by static, like the spindle body.
Sure there would be a workable method of dust extraction for foams just using electrostatics :-)

Its very soft, but too slow or too deep seems to chunk bits rather than cut, sharp wood router bit is fine, internal grain of insulation foam is quite bubbly, for finer grain want proper model board.