I used Sphagnum Peat Moss mixed with construction sand. Then when I was cleaning out the spent growing medium in my veggies planters, I tossed that in, too. I also dig up dirt, complete with weed seeds and bugs and mix that in also. The chickens all love it, especially my alpha roo, who can be seen in the dirt bath all by himself, flipping dirt over himself, oinking in guilty pleasure.