Matala MAT4PK19X24 Quarter Sheet Pond and Koi Filter Media (4 Pack), 19" x 24", Multicolor The open, highly aerobic tri-dimensional structure of Matala Filter Media promotes healthy water conditions Ease of cleaning in in a wide variety of filter Designs Mats are self-supporting, form-stable, rigid and non-brittle This is simply the most effective, longest lasting, crush resistant filter material available today!