Cellulose tends to catch larger particles on the surface (see the Donaldson images), where they embed, or they can fall off and collect in the bottom of the can (see Wayne's recent Durango filter dissection) which risks them being washed through the engine during a bypass event. As Donaldson notes, the finer particles will embed in the media, but as the larger particles block the holes, loading up the surface, the flow begins to suffer, as does the efficiency if the filter ends up going into bypass. There is only a single layer of cellulose, so the media cannot provide significant or refined depth filtration.
We already went over the material covered in this presentation back when you were Hubert P. Farnsworth in 2019, but as a refresher, this is the material from Cummins:
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The original Ultra had two distinctly separate layers of synthetic media (probably not as complex as the Stratapore, but these are passenger car applications) providing true progressive depth filtration.
The "new" Ultra has a dusting of synthetic media as an outer layer, to capture and hold the larger particulate (increasing holding capacity) but the 2nd layer is a cellulose or cellulose blend media, meaning it lacks the advantages in flow and holding capacity that its predecessor had. They've worked to try and mitigate this by using more media, making the back layer more similar to that found in the PureONE.
As I've noted several times now in this thread, by integrating inexpensive cellulose, they've decreased the cost of production both through the media itself, and through construction, allowing the product to be manufactured in a conventional fashion, since the step of fitting the wire backing is removed.
As already noted, the two mitigation mechanisms employed to keep it a "premium" filter are:
- Synthetic "topper" to increase holding capacity
- High efficiency cellulose (or blend) backer to maintain efficiency rating
Neither of those things turn it back into the premium filter it was previously.
As Cummins details, a synthetic progressive depth filtration filter offers a plethora of advantages, but they require numerous extra construction steps, making them more expensive to produce.