Litter-Robot simply requires clumping litter. We recommend a high-quality, standard-weight, clay-based clumping litter, such as our GreatLitter. Some silica gel litter beads and crystals can also be used with Litter-Robot, as long as they pass through the screen. Alternative, plant-based litters may also work, but these tend to form looser clumps that can cause condensation in the waste drawer. When using a plant-based litter, we recommend emptying the waste drawer and cleaning more frequently. Litters that do not work in Litter-Robot are the strictly absorbent, non-clumping or loose-clumping litters, newspaper-based litters, and absorbent wood pellet litter.