I've had my heavybag outside for about 2 years. It's supposed to be 100lbs but I weighed it at 120lbs. So I opened it up today and sure enough it was wet, though not moldy, but it had another surprise for me...there were about 20 little maggots inside. So I dumped the entire filling (shredded cotton and sand bags) in the trash and washed out the bag. I'm never keeping a bag outside ever again.