It's your own mini foam cutting heat saw. Don’t use your wife or mom's good steak knives to stain with flame and cut your foam. Keep on her good side by purchasing this inexpensive knife and you won't even have to wash it afterwards!
We use this knife by heating it in a torch (or stove burner) to slice through foam in hard to reach places (like battery compartments).
For general foam cutting without heat, use the other knife with retractable blades- it is THE best all around foam cutting knife, period!