Comment by trenchpilgrim 2 days ago
I began noticing this about seven or eight years ago when the oil filters I bought changed from official ones to obvious counterfeits (certain pieces were missing entirely + media was much thinner than the real ones). Had to switch to a local auto parts supplier to guarantee the correct part.
Not always - some passenger vehicle filters have exposed media. An example GM filter: https://parts.gmc.com/product/acdelco-gm-original-equipment-...
My current car has a traditional steel-can filter. I cut those open after oil changes to inspect for debris.
It was a suzuki with a paper filter cartridge you load into a metal cylinder that is part of the engine. So you can see and feel the media.
How did you notice that the media was thinner? On passenger vehicles at least, the filter media is in a stainless steel cup that precludes examination.