I work in a parts store and I sell parts master and wix filters with the occasional MANN and Delco filter making apearances (MANN for certain foreign cars and AcDelco for all the dyed in the wool Chevy fanatics) I know that wix has black filters and white filters throughout there lineup, and as far as I know black is light duty and white is commercial duty. (Possibly subject to old/outdated packaging)
This has got me interested in cutting open some filters tomorrow. : D
To the guy who asked why these things are still on the shelves I have two things to say. First off shops love cheap bulk filters and an overwhelming amount of mechanics either have no say what filters the shops use or really don't care. I'm sure quite a few of them rarely stop to think about the inner workings of a filter.
Second point is price. We might sell a wix filter for 2.50-3.00 dollars more than a parts master equivalent. An awe inspiring amount of people in this town are disgustingly cheap and demand parts master oil, parts master filter and any other cheap consumable even if they have the option of getting an option like Castrol synthetic blend oil for seventy five cents more a liter.