Vermiculite is what we use as egg incubating medium for all our tortoise eggs. We use and offer a fine grade vermiculite (free of asbestos). Our typical egg incubating mix is 200 grams dry vermiculite to 140 grams water (10 to 7 ratio, by weight). This is for just shy of 1 cubic foot of vermiculite, which is plenty for several clutches of tortoise eggs.