Substrate ratio to lower humidity?

[Bogertophis]

I think some things can survive freezing but not baking. It's just not fun to bake a bunch of dirt, IMO, but your choice. Paper doesn't mold...but mold spores abound in dirt, just saying.

Sand, even play sand, is abrasive- it can get under a snake's scales & cause nearly-microscopic scratches which then may become infected- sometimes to a serious extent, so I'd avoid using sand.

I personally don't like newspaper because it's not very absorbent, doesn't offer any traction for snakes, & snakes end up sliding thru their excrement, though if you put a second layer on it, that would help.

I keep mostly colubrids that don't need so much humidity- for convenience, I line tanks with paper towels, & over that is a thick layer of 50:50 paper shreds & Carefresh. This way I can spot clean, & when it's time for a total change, I just roll up the whole mess in the paper towels underneath- very few of my snakes burrow at all. That would change the equation.

Substrates are not "one size fits all"- do what works for you & what you're keeping- & what keeps them healthy, of course.