I run the low density (black) to keep media separated and avoid any egg crate. If you are trying to trap small particulate you will need the super high density (grey). I opted not to use that fort mechanical because I have heard others complain about it clogging and being difficult to clean. My mechanical is handled elsewhere so it is a non-issue for me at least.
IMO (especially at $35 a sheet) I would leave it and see if you like it. You can always cut it into strips so you double the material wall thickness. That would accomplish the same end without having to order another sheet.