In Europe hemp is a popular substrate. Those that use it highly recommend it, but its unavailable in the US. Some people are using aspen instead and it seems to work well. Both may work for some species, however they are not suitable for Russian tortoises.his is by far the best substrate. The amount of moisture can be easily regulated. Also it easy to create a higher moisture/humidity (substrate moisture is more important than humidity) area as well as a dry area in the same pen.