I don't use really finely shredded. Its more like little strips about 1/2" wide and 2" long.

I can see the mess issue though. Maybe I can wean him down off the shreds. I definately experienced the humidity thing which is why I had to add in some wet paper towel wads.

I've never used aspen and I don't recall seeing it in the stores around here. Is it soft? If its what I think it is it always looks like sharp little wood splinters to me (in photos)