Catsan Crystals Catsan Crystals are made from highly absorbent silica gel crystals. These cat litter crystals provid fast acting absorption of liquids, as well as complete elimination of bad odours for your cat litter tray. Urine is absorbed into the crystals and once they've reached their full capacity, they'll become clear – usually after 2 weeks with the 2kg bag and, 6 weeks with the 6kg crystals bag. If you'd prefer a clumping cat litter, check out Catsan Ultra! Are you looking for something to help you remove urine odours and stains from anywhere, around the house? Check out Urine FREE!