I wouldn't use any kind of bath or kitchen sponge in an aquarium filter because they might be processed with some kind of chemicals. I'm not that familiar with fluval filters, but I've run AquaClears with filter floss instead of sponges and they worked fine.
I'll move your thread over to the Hardware and Do It Yourself section where you should get some very good information about your specific filters.
Kitchen & bath sponges are often treated with anti-fungals/bacterials. You can often find larger sheets of sponge in the marine or pond section of a larger shop.
Car wash sponges, the cheapest you can find, are not treated. While they are not open cell sponge, which is what works best they will work in a pinch. I've seen plenty of aquarists stick half of a dog bone shaped car wash sponge over a power head for a filter.