By no means am I an expert but I found I can get the humidity to around 75% if I put a ziplock plastic quart bowl full of damp sphagnum moss in there and place a t-shirt over the screen. If I remove the t-shirt it drops to about 55 to 60% and if I take the moss out (but leave the tshirt) it hovers around 50%. Whatever it is the moss seems to have the biggest impact on things. At least for me.