Yes, you can add filters in this holder, two to be exact and as far as the thickness of the filter goes, I have no idea. I own several different name brands of filters which I use in this holder without any problem. All the filters I own fit nicely into the holder and for myself, I have never really given any thought to the filter thickness, however you will be able to fit only one filter per slot. Sorry I cannot be of more help but this filter works great for my photographic needs.