Chubby moss also known as pin cushion moss is a live plant, which with the right environment will thrive and help create humidity.
It is best kept at around 24 - 32C, with a humidity of over 50%. 
Moss is a living breathing part of your enclosure, and so will help keep humidity levels up, and also add fresh oxygen into the enclosure from photosynthesis.
 
Please note:
We recommend lining all wooden enclosures with a waterproof liner before placing substrate in to preserve the life of the enclosure.
Although we throughly check all substrates, we do recommend that any substrates that are a natural product should be screened to ensure any unwanted items are removed prior to adding to your tortoise's enclosure.