What the substrate needs to do
Use a clean soil-style substrate for Pterinochilus murinus that can hold its shape without becoming hard, dusty or permanently waterlogged.
For Pterinochilus murinus, the substrate in an Orange Baboon Tarantula enclosure should support normal movement and retreat building. Heavy decor must not be able to collapse if the spider digs underneath it.
Depth
Orange Baboon Tarantulas are terrestrial, so give Pterinochilus murinus enough substrate for normal digging while also keeping the fall distance from the lid low. A stable ground-level hide should sit securely on or in the substrate.
Match substrate depth to the current size of Pterinochilus murinus. Small slings and fossorial individuals often use proportionally more depth than a large settled terrestrial adult.
Moisture
For Orange Baboon Tarantulas, keep the enclosure mostly dry, with surface with access to water and a modest moisture gradient; avoid stagnant wet substrate. Add water in a controlled area and judge how the enclosure changes over several days instead of trying to keep every centimetre equally wet.
Substrate moisture for Pterinochilus murinus should work together with ventilation. Persistent condensation, a stale smell or widespread mould usually means the setup is staying too wet.
Compaction and stability
Press the lower substrate layers firmly enough that a retreat or burrow for Pterinochilus murinus does not collapse immediately. The upper surface can remain looser where appropriate.
For Pterinochilus murinus, keep rocks, heavy cork and ornaments in an Orange Baboon Tarantula enclosure low and secure so excavation cannot undermine them.
When substrate needs replacing
Spot-clean waste and prey remains from the Pterinochilus murinus enclosure. Normal digging, webbing or rearrangement by the spider is not a reason to replace clean substrate.
For Pterinochilus murinus, replace all substrate for an Orange Baboon Tarantula only when it is fouled, contaminated, persistently mouldy or no longer structurally usable.