I hate using aspen with my BP because he passes so much liquid when he defecates. I'll get a TON of condensation and ammonia smell because the aspen doesn't absorb it and it sits underneath on the bottom of the tub. I of course try to be vigilant, but about once a month I switch to paper towels, which makes clean up MUCH easier and keeps me from missing things and getting unhealthy condensation/ammonia buildup.