<a href=showthread.php?s=&postid=10418502#post10418502 target=_blank>Originally posted</a> by manderx
it looks better than bare glass. it reflects light back up to the corals. it spreads the weight of the rock out so it's not a whole stack resting on just a few tiny pressure-points. plus it keeps the rock from sliding around.
<a href=showthread.php?s=&postid=10481818#post10481818 target=_blank>Originally posted</a> by AIMFish
Type POLYPROPYLENE SHEET in the search on MSC's site.