Rena Microfiltration Pads with Biocomponent are new & improved. Designed to fit the Filstar Xp range of external filters they feature graduated hole sizes which allows for increased cleaning. For ultra-fine filtration and polishing place a pad in the last filtration compartment. Size: 160x160x14mm Cotton pad with gradual thickness that removes the smallest particles before the water is returned to the aqaurium. Due to its dual density, its ability to remove dirt is 2 times greater than conventional cotton pads.