Filter Foam is a universally applicable pond filter material that removes visible dirt particles from the pond water. It is available in a fine, medium and coarse structure and in many different formats and thicknesses. Using scissors or a knife, you can easily adjust the foam material to make it suitable for your filter. For best cleaning results, we recommend using several layers of filter foam, from coarse to fine.Filter Foam white has a fine structure.Filter Foam blue has a medium structure.Filter Foam black has a coarse structure.