I use tissue/kitchen roll with every thing: ootheca, nymphs and adults, (unless im setting up a multi species vivarium, not just mantids) it lends itself perfectly to however you have to keep mantids.More humidity = more depth of tissue & spray.
Less humidity = less tissue & less spraying.
If its pressed into the base when wetted it pretty much stays like it and prey is less likely to hide under it if you feed crickets, roaches and meal worms.
It becomes obvious when its soiled, especially white tissue and is easily changed with out carving out great chunks of the countryside.
Its also cheap as chips