pillow moss is not the best terrarium moss. 9 out of 10 times it will die.

If you want a fairly good terrarium moss, try java moss. it thrives in moist to wet conditions. some selaginella, although not true mosses, do very well in terrariums. sphagnum moss may spring back to life in wet conditions but soon dies, as it is a temperate moss.

you could also try some moss-like plants such as babys tears. however, it will soon become a weed, so prune it regulary if it becomes a pest.

~chris