Sand substrate 200 ml
With a simple 'test-tube-in-a-box' setup it's often not a bad idea to add a thin layer of clear sand, adding benefits like ease of cleaning, stability and helping out the ants in some ways..
Cocos substrate 2 liter
The most popular substrate material for ants because of it's water-retention capabilities. Sold as solid 'peat' blocks, just soak it in water to loosen it up and make itl expand enormously.