BioGuard Skim mor uses a mycelx coated material which traps oils, cosmetics, lotions, pollen, and pieces of fine debris your filter may miss. These impurities can dull your pool water, cause a waterline build-up, and even clog your cartridge or DE filter. This product stretches to fit virtually all skimmer baskets. It is proven to extend the life of the filter and to reduce maintenance time. Other skimmer socks are not coated with mycelx, but skim mor is.