If you really want to see what free breathing looks like take a foam filter, a K&N, and a velocity stack and hold them up. Whichever allows the most light through will breathe best, whichever lets the least through will likely filter out dirt the best. I think we have a winner at both ends of the spectrum here. Not to mention one that seems to fit in between them working better than one and worse than the other again at both ends of the spectrum.