When adding substrate to your frog's enclosure, you should be looking to use substrate that is the most similar to the ground conditions of your frog's natural environment. Consequently the specific substrate that you use will depend on your individual species of frog; however, natural soil substrates are often a good place to start as many captive frog species originate from rainforests and soil is particularly good at retaining moisture and consequently humidity levels.
Ideally, your glass terrarium should include hydro drain to ensure there is the optimum moisture to the substrate above, meaning live plants will thrive as well.
At Swell Reptiles we have an extensive array of great value, frog substrates so why not browse our range and select the perfect substrate for your pet!