two ball pythons in one tank?

[Foschi Exotic Serpents]

I am curios then, why the switch to aspen?

Well personally I don't use either.. To answer the OP's question: I use either paper towels or cypress mulch for my snakes. Depending on what's going on. I switch between the two depending on breeding season, or if one of them goes on feeding strike and I'm changing things around to get it to eat. I switch to paper towels for gravid females simply because it's cleaner and easier once the eggs are down. Paper towels for snakes in quarantine to make it easier to spot mites.

I don't use aspen simply because it molds incredibly fast if you need to mist it. Cypress is mold resistant and is a lot cheaper at home depot in big bags.

I use pine for my rats because it controls odor and moisture better than anything else I've found. It's also a lot less dusty than pine pellets and is much lighter in weight.