I use a mixture of vermiculite and perlite. In the past I've used all Vermiculite, all perlite, Sphagnum moss, Coconut coir, and even potting soil. They all worked just fine for keeping the humidity level where it was supposed to be which is the purpose of the incubation medium in the first place. The mixture of the vermic and perlite to me seemed easier in the long run because I didn't have to babysit it as much and constantly check on the moisture levels and add more water if it seemed to be drying out. It just seems to hold moisture for a longer period of time.