Sheet moss is a live plant, which with the right environment will thrive and help create humidity.
It is best kept moist 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.
You will receive one sheet of moss
 
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.