Clumping litter is one of the market's most popular types of cat litter. They are made from clay or other absorbent materials that form clumps when they come in contact with moisture. These clumps can be quickly scooped out, leaving the rest of the litter clean and fresh. Clumping litter is effective at controlling odors and is easy to maintain. However, they can be more expensive than non-clumping litter and are not biodegradable.