Are you talking about substrate for pygmy chams? If so, the common recommendation is hydroton, screen, carbon, screen, and then organic potting soil/peat moss/sphagnum combination plus leaf litter and sterilized vines /twigs/branches. This allows for optimum excess water to be absorbed and filtered rather than becoming a soupy mess on the bottom of the enclosure. Don't forget plenty of live plants to hide among.
If you are talking about true chameleons the answer is ... no substrate.