Our rack isn't one species only at the moment, so it really depends on the individual snake, but also what I have available at the time (I like to buy things when they are on sale ).

I like aspen for the low to mid humidity range, and I have ecoearth/forest bedding (coconut) + moss mixed in to maintain high humidity for the BRB. I've also used a mix of ecoearth and some form of reptile bark because I like how it looks, but it also makes a nice consistency for the baby dumerils to burrow in and push around. I reserve my newspaper and spare ads in the mail for the bottom of my bird cage.