I am currently a month into using a bath towel in my 40gal glass tank. I was using cypress mulch.

So far, I have been happy. Makes it really easy to clean the tank frequently without lots of cost. I have also been putting a wet, folded washcloth on the hide under the CHE to bump up the humidity. Truthfully, the humidity has been holding better with this than using the mulch and misting at least once daily. Cheaper, too, because then I just throw the towel and rag in the wash once a week and rotate in a new set.