Aspen, cypress mulch and coconut fiber are great.
Avoid pine, cedar, sand, calci-sand and walnut shells.
Corn snakes are primarily found in eastern United States. This climate includes plenty of brush, wood, clay, and somewhat dry soil, which gives us a good idea on what to base corn snake substrate on. Keep in mind, however, that pine and cedar should always be avoided. Although it’s naturally found around the same areas as corn snakes, they let off strong fumes which cause respiratory issues in reptiles when enclosed in a small space.
The most frequently used substrates for corn snakes include aspen, coconut fiber, and cypress. All three of these bedding options allow for burrowing, aesthetics, and they can be mixed to create an even nicer substrate. For example, cypress and coconut fiber are frequently used together. Paper towel is a more sanitary, yet less visually appealing option, nor does it allow for any digging or burrowing.
A juvenile corn snake may need just a couple inches of substrate, however, for adults, adding even more can be very beneficial to allow the corn snake enough to feel comfortable, and even burrow if interested. I found that young corn snakes are often more interested in burrowing than adults.