It just stays wet and starts to mold with a white fuzz if you don't change it all out. I use Aspen and spot clean constantly, then clean and sterilize all the tubs once a month and I've never had any problems. Carefresh tubs needed to be cleaned and sterilized every week or two or the stuff looked bad and had a chance of getting the white fuzz. I just don't think it's very obsorbant at all when compared to shredded woods by volume.