The base medium doesn't have to absorb water at all. It's only about adding humidity in the container and as long as the cakes aren't sitting in water, moisture remains high. There may be a little water under the styrofoam and moisture is beading up on the sides of the container. Bottom line- it worked, they are fruiting with good results and I didn't have to buy any perlite.... so don't knock it if you haven't tried it.