Thanx Jim. I could not get a response from the manufacture and my supplier told me the opposite after first telling me it did not matter.

So I understand correctly - do you mean the "plastic" type material faces in and the soft "cotton" type material faces out against the sponge filter?

I use a Remstar Auto A-Flex system one. It come with 2 filters a grey sponge and a white pollen filter. The pollen filter goes in first then the sponge filter. What I can't find out is which way to face the pollen filter. Does the soft side face in or the hard side? Thanx for your help.