Finest-Filters DIY Fine Foam Media Sheet for Aquarium and Pond Filters Our DIY Foam Sheets can be cut down to fit any aquarium or pond filter Size of this DIY sheet: 18inches x 12inches x 25mm thick Grade of this Foam: Beige 30ppi Reticulated Aquatic Foam This foam allows beneficial bacteria to colonise, which break down wate, providing biological filtration