[foxx]

http://s220.photobucket.com/albums/dd61/fox336/?action=view&current=PA230002.jpg
http://s220.photobucket.com/albums/dd61/fox336/?action=view&current=PA230001.jpg
Hay

 

[Forensic]

Hay will likely be uncomfortable, may mold, and won't really do anything to absorb moisture or odor.

 

[Mana]

Along with the things Forensic pointed out, from what I remember of hay from my guinea pig, it has a very strong smell. That would be my biggest concern with using it for rats, because they have such sensitive respiratory systems.

 

[chrisstrikeagain]

Hay isnt a good beddin for anythng. It oesnt absorb and makes a odor by so.
It also is undigestible to rats and isnt comfortable. And may mold when peed on, which may kill your rat or get them sick.