hot knife

so ive been trying foam builds but my hot knife doesnt cut that well. I think its probably the blades. but does anyone know any strong hot knives that work?

we just bought a cheap one from the hardware store what came with a bunch of attachments. As far as ours is concerned the sharpness of the blade doesn't matter, the heat seems to do all the work. Its also amazing for separating hot glue without damaging what its attached to (so long as you don't touch meltable stuff with it). Might be that our one gets hotter, its advertised as a wood burning tool as well. It's not temperature controlled or anything just plug in and wait till hot