Im guessing its for ball pythons. If it is then 50-60% is the proper humidity. The holes arent only for regulating humidity, but heat also. A tub with no holes in the back to allow heat to come in can remain virtually uneffected by the heat tape in the back. My room is usually around 68-70 degrees and i have a rack from repti-racks with boot boxes in it. The back of the tubs are almost completely covered in holes to allow the heat in. I set the heat tape in the back at 107 to obtain the proper temps for what in the rack.