The kiln dried feature is part of the America's Choice product. It is kiln dried for maximum absorbency, multi-screened to remove irritating dust. It is used in horse stalls. Horses are very sensitive to dust and can easily get respiratory ailments from dusty bedding, so this is important.
With the bull snakes, as they grow and make yet bigger wastes, the aspen is not doing as good a job as I would think the kiln dried pine would at odor control. I keep the cage clean but the aspen seems always to have a sort of sweetish smell, like a faint zoo smell. I am seriously considering trying the pine with the bulls, at least.
One time I went to buy the America's Choice for the mice but the feed store was out so I had to buy a different product, and that wound up going directly into the garden, as it was very damp and smelled very piny.