NEWSPAPER: Pro- cheap, easy to replace, completely safe, can be used as a "hide"
Con- Not eye pleasing (when soiled), not very absorbent, cannot be spot cleaned.
REPTI-BARK: Pro- Eye pleasing, easy to spot clean, holds humidity well, can be burrowed into, can be utilized in shedding process.
Con- bags of repti-bark have been known to have mite eggs (bags must be sprayed with proventomite or other mite removal products before putting into tank), pain in the butt to remove from tank and completely clean once a month as recommended, difficult to reduce humidity levels if too high.
ASPEN: I have not used this but what ive seen it is not very eyepleasing when soiled, the snake can move large amounts of the bedding with it when the snake moves leaving parts of the tank with uncovered areas, it is recommended to not feed your snakes with the aspen because it is harmful if swallowed (that's according to the aspen product i looked at...other aspen bedding manufacturers may have different recommendations).
other people may have different ideas/opinions about the products listed. this is only my observation in using the listed substrate and may be different than the conclusions of other people.
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0.0.1 Colombian Redtail Boa
1.1.1 Sumatran Blood Pythons
1.0 Black Blood Python
1.0 Dumeril's Boa
0.1 Coastal Carpet Python
0.1 Jungle Carpet Python