Vermiculite Substrate?, for reptile eggs and invertebrates needing high humidity over substantial periods. Where a highly humid environment needs to be stable for extended periods of time, Vermiculite Substrate has few competitors. It does not rot or support microbial growth. It will not leach toxic chemicals and it holds incredible amounts of water for its weight and volume.
  
It is, however, quite fragile and only small invertebrates like young spiders and scorpions of species that like wet environs should be kept on it. The major use is to hold incubating eggs, a task it excels at.