I read about filters and what Carrier recommends, since I have a Carrier HVAC system. When the installer came to do his annual maintenance and switch the old filter for the new one, he said they usually use and recommend a MERV 8. I realized, having done my homework, that they're just being cheap. His argument was that mine is so tight that it's harder on the system. I don't think so. I have asthma and want the best filtration I can get. The fact that Carrier recommends a 13, was all I needed to know. It's a nice, sturdy filter.
My Observation-There doesn't seem to be uniform spacing between the folds within the filter. Even though this probably doesn't mean much as far as the make up of the filter, it most probably has some effect on the functionality and/or efficiency of it.
A wee, little bit smaller and thinner than brand name filters but cheap enough I can replace more often. I get a higher MERV rating with these filters.