Kiln Dried Pine
Kiln dried pine is safe to use as long as its low in dust. you can get it at most farm stores, such as tractor supply and ward lumber. You can also get it from the pet store, though it's more expensive. make sure its kiln dried and low in dust, one time a accidentally got regular pine, and my gerbils noses got all red and bumpy, I immediately caught my mistake, and got the right brand. It should be aired out by opening bag, and letting sit for at least a week. I personally don't recommend this bedding type for young pups, or pups that are weaning, due to slightly higher dust levels than aspen, though I find it works well for teenagers and adults. I use it for most of my non breeders, and no gerbils have encountered any allergies.
good for burrows,
can have a strong pine smell,
can cause respiratory infections in weaning pups,
sometimes may contain to much dust.