I know I've read about of Opel owners using Fram oil filters, I have myself. Well while looking for oil filter "ratings" for my motorcycle, I came across the following link. This guy bought a bunch of oil filters from several different manufacturers, cut them open and evaluated the materials used and construction methods. The link below shows the report on the Fram oil filter, not very good. There are links provided to other oil filters tested on this page. Check out the K&N oil filter for comparison sake. Just looking at the pictures says a world of stuff.
http://www.twocreeks.net/toby/oil_filters/fram.shtml
This evaluation project was done on motorcycle oil filters, I don't know if this corelates to automotive oil filters at all, but it does get one thinking. I did cut open a motorcycle Fram oil filter I had, looked just like the picture in the report. I'm not using Fram oil filters on my motorcycle anymore.
Has anyone out there ever done a similar comparison themselves of automotive oil filters? Inquiring minds want to know.