I have 2 custom 3X2X1.5 wood cages that I use Reptile Prime in about 1.5-2" deep. I found I blocking off some of the air flow to help retain humidity from dropping too quickly. I did make it with extra holes so I could plug or expose as needed. Also the cage with a little more substrate seems to hold humidity a bit longer then the other one. There is a noticable difference with only half inch difference in depth.