I did some research on this a while back and learned the FILTRAN branded filters are 80um, which is about as good as it gets for a pan filter. I don't know the specs for any other brands but SPX Filtran supplies some of the best ATR filter media and it's used by a number of other mfrs. I had some contact with two engineers at Filtran, which is how I got the 80um number. My thinking was that I would go with the brand I know the specs for, especially since that's about as good as it gets. Many pan aftermarket pan filters are 100um.