PZEV (Partial-Zero Emissions) and ULEV (Ultra-Low Emissions) are just emission ratings. A PZEV is the more economical choice as it is suppose to be cleaner and better for the environment. The ULEV could provide slightly better performance, but it won't be enough to notice. If your state requires emission testing be sure you get the one that is required. In Oklahoma, we don't have to worry about the emission tests.
I haven't replaced my cabin air filter so I am interested to know as well.
Thanks Stormtrooper. But I should have been more specific. I know the difference between the two models. I was asking, What is the difference between the Air Filters? Some Filters work for Either. Some work for Both. ???
I'm pretty sure the ULEV and PZEV filters will be interchangeable. Although the PZEV model of Elantra has two air filters while the ULEV's have only one. If your trying to replace a PZEV the chances are that you will only be able to replace the bottom filter. The bottom filter should be the same fitting on both models just different emission ratings.
I'm guessing the two air filters on the PZEV restricts more airflow causing the performance to decrease slightly and "go green". The top air filter isn't easily removed. Honestly, I don't know if it's replaceable. I use a K&N air filter (bottom) with the top filter removed. Removing the top could void the warranty.