Left to right are Suby blue, Mobil 1, and our favorite, PurOne Purolator.
Notice the size of the filter media, that M1 is a joke. Also notice the inlet holes around the base of the filters. The Subaru has three to four times the opening area to allow flow. We all know these engines need alot of flow. The thickness of the canister is also surprising. PureOne was the thinest, then the Subaru and the M1 was the thickest.
I also opened a Napa Gold spin flow, and a "Mighty" brand filter. The Subaru filter seemed equal or better quality than any I have opened up, and has the ability to flow more oil judging by the base openings and media size. Also note the relief spring in the subaru filter was much, much softer than ANY of the filters I opened. In fact, the Purolator has some type of disk relief valve that looks questionable. These are just some samples of filters I have taken apart. I had a fram and the Subaru side by side and there was no resemblence what so ever, and the fram had a rediculously tight relief spring, along with the thinnest can I have ever tested.
The third thumb nail is the relief valve on the Purolator. I have yet to take that apart to see how it works.