you must not have read about the problem very well or something. they are trying to raise the rh in a grow BOX so were is the towel and fan gonna go? and the cold air humidifier ? and i didn't say that was the only way to do it. but heat and water create whats called water vapor and is then released into the atmosphere thus creating humidity. when the air is cooling at night the humidity goes up due to water vapor starting to condense and thus creates dew on you grass. common sense for most people because it happens around you all the time. happy times and good luck to you