Our #1 selling litter Ultra has superior odor control and is perfect for multi-cat families and those cat owners with sifting or mechanical litter boxes. Dr. Elseys Ultra Litter is a unique formulation that combines the heavy non-tracking granules of the Classic Litter with a medium grain clay. The result is an excellent clumping litter that prevents moisture from reaching the bottom of the tray while providing a clump that will not break down. As seen on BuzzFeed and in the New York Times Wirecutter.