How 2 Cut Foam?

A minor rant: Something I haven't really seen anyone talk about, but has been troublesome for me, is the cutting of foam in terrain building. It's always glossed over and nobody ever seems to have any difficulty slicing foam into whatever shapes they need. But for me, I've had a hell of a time trying to get a clean cut on both foamcore and insulation foam.

A reasonably clean cut.

A completely horrible cut.

Even when I feel the blade sink in smoothly, it often ends up jagged in some way, and it's pretty common that it doesn't sink in smoothly anyway. Foam also seems to dull blades alarmingly fast, and I've even noticed a blade that started off cutting foam quite easily get dull and start to struggle after less than ten minutes of cutting.

I'm obviously doing something wrong, and it's something I'll pick up with experience, but for now it's still really annoying. I'm still trying out different methods, as I'm hoping that there's a good way to do this besides just starting with a brand new blade every time.