Cats living inside a home without any possibility of outdoor access have to defecate in a litter box. To suit the cats' needs, several recommendations seem to be agreed upon. The litter box has to be clean and in a calm spot easily accessible to the cat. It has to be in a size that fits the cat. The number of litter boxes has to be correlated with the number of cats present at home as well as the size of the household. The box should contain a substrate that allows the cat to comfortably dig in it. The box should be of a size and the litter of a style that the cat can defecate without soiling itself in the process. The litter should be sufficiently absorbent and manage odor. Facing a great range of commercial possibilities, cat owners have to make a choice. There is no standard recommendation about substrate. The study sought to identify preferences of cats regarding a specific type of substrate by comparing clay granules, silica in microgranules, silica granules, and wood pellets. The study was divided into 2 phases. Eighteen cats were selected for the first phase that lasted 4 weeks. Three strictly identical and uncovered litter boxes were presented to the cats. Each box contained one of the substrates (i.e., clay granules, silica in microgranules, wood pellets). The cats demonstrated a significant preference for the clay or silicate substrates (no significant difference between them) as opposed to the wood pellets. In the second phase, 12 cats were observed during 2 weeks to compare their reaction to clay and silicate. Here, the same grain texture (i.e., granules) was used. The cats showed a significant inclination to defecate into the clay substrate, instead of the silica substrate.