meant to add, this is for chickens and not plants. :

I've never known there to be a difference. I suppose what ever is finer would be warmer. But that is a guess.

Kitty

I think they would be much of a muchness. The warmer one would, I think, be the fatter one - grain stems are hollow, and the larger the thickness of the stem, the more air and the more insulation. I don't really think that the differences would be major ones, though. If either type looks to have been wet, and is damp, discolored or dusty, I would get the other one.