I user Herptopia in my pro-line cages and it is shipped very dry. It's not like some of the other coconut-husk products that are packed together tightly and need to be soaked in water to break apart. You can just dump it in to your tubs fresh out of the bag without wetting it down, so it shouldn't cause any extra humidity. As long as your tubs are holding the correct humidity without substrate, I don't imagine it would change by adding herptopia.