Composting toilets use organic materials to cover the waste deposits, improve the composting process and to reduce or eliminate odors. Almost any type of organic material can be added to a composting toilet, as long as the final or top material is "brown" instead of "green"--carbon rich materials that do not smell as they decompose. Fruit and vegetable kitchen scraps can be added to the composting toilet for example, but since they will smell badly as they decompose you need to add other materials to neutralize those odors.
The smaller your organic material is the better it will work for keeping unpleasant odors at bay and covering the waste deposits.
Sawdust is an excellent material to add to composting toilets because it absorbs liquid well and it's fine enough to cover odors and sights appropriately. Sawdust also decomposes quickly, helping to create your compost over shorter periods of time.
Peat moss is also quite small and makes an excellent composting toilet additive and cover material. It decomposes well and adds rich nutrients to help create fertile finished compost.
Hay and Straw
Hay and straw can be used as organic materials in a composting toilet, and they do an excellent job of creating natural air pockets that help the composting process accelerate. Hay and straw are bulky though, so when used alone they don't cover deposits and odor as easily unless you use large amounts at once.
Hay and straw are often used as the beginning, or base material for a homemade composting toilet. Filling the toilet space 1/3 to 1/2 full before using it creates a thick bio-filter layer that works well as a starter base for your composting process.
Hay and straw are also popular to use as the top covering material for an outdoor toilet compost pile because they insulate the pile from freezing in winter as well as prevent too much rain from entering the pile. They also work well as a top cover to ensure no odors escape.
Dried leaves and leaf mold are another popular organic material to use in composting toilets because they also neutralize odors effectively, and when dry the leaves can easily be crumpled into smaller bits which cover the toilet deposits well.
Shredded paper is another material that works well in composting toilets, but because it's not often shredded fine enough you may need to use a lot of it at once to control odors.
Some commercial composting toilets require you to use their own mix of organic bio materials instead of the standard materials mentioned above. Consult with your owner's manual before choosing alternate materials to use because they may void your warranty or cause malfunctions with your toilet.