Well, I discovered today that the same can be said of 2mm craft foam. I wanted to help a visiting friend by making her some stamps. She bought a sheet of pale pink foam from the same place I buy mine and to all intensive purposes, it was the same, except mine is red.
We spent hours trying to cut the stuff. Different speeds, pressures, blades, mats. You name it, we tried it. None of it came out clean as I am used to. All of it had little wisps.
I then decided to use some of my red foam. Cut like a dream with the same blade and settings that I had been using on the pink. Result - perfect cut. On my Silver Bullet I used a speed of 500 (!), a force of 200 and an extra long blade ( a mistakenly purchased cheap 24 mm long one), on number 1 in my click holder.
That little dot is 0.5cm across. So now you know, it may not be you when it all goes south!