It is filled with cat litter, a granular material that absorbs moisture and that is readily available from supermarkets and pet stores. "Clumping" litter forms clumps to absorb urine, which can easily be sifted out. Sand can also be used, although commercial litter is popularly considered superior, as it clumps better and is often treated with odor-masking chemicals that can reduce the unpleasant odors associated with a litter box, although the clumping and chemical additives are considered by some to be detrimental.
The most basic type of litter box is a plastic tray. More elaborate models are enclosed, which provide some privacy to the pet and better odor control, as well as keeping the litter out of sight. To facilitate emptying the litter box, plastic liners are available for purchase. These are placed in the litter box before putting in the litter. When the litter needs to be changed, the owner simply lifts the liner, ties the ends, and discards the liner with the dirty litter.
Recent developments in litter box technology have made further improvements to the emptying procedure, which can be the most unpleasant part of owning a litter box. Some models have electrically controlled combs that automatically scoop the dirty litter clumps out of the litter box into a sealed container after the animal has used it. Other models can be shaken to move all the dirty litter clumps into an easy-to-remove tray.
It is advisable to place the simple tray-type litter box on some newspaper, as most cats will kick some litter over the edge of the tray when using it.