Answer:
You can tumble in it, roll in it, burn it, animal eat it. Used to cover floors, still used beyond stall doors. Freshens whatever it is placed on. Absorbs whatever is poured into it.
They're up near the sky, on something very tall. Sometimes they die, only then do they fall.
Tall in the morning, short at noon, gone at night. But I'll be back soon.
As soft as silk, as white as milk, as bitter as gall, a thick green wall, and a green coat covers me all.
What is often returned but is never borrowed?
I repeat only the last word you say. The more I repeat, the softer I got. I cannot be seen but can be heard. What am I?