This pillow will never go flat so long as you don't do anything to compress it. It provides slightly more resistance than air. It does rebound very quickly, but one by itself is inadequate for me. If I had three or four and stuffed them all into the same pillowcase, it would probably work out ok. I am a side/belly sleeper and need other firmer pillows to bolster this one up to be usable. However, it is very comfortable to the touch.
I do have some concerns about the fragility of the pillow. It will shred very easily and after a few linen changes small chunks have begun flaking off when I change the pillowcase.
I found the zippered cover that came with it to be counter-productive to the soft pleasant bed I was trying to make. It is very coarse, stiff, and makes crinkly noises like a hospital pillow--or a paper bag. The coarseness transmits through the pillowcase I put it in, but without the cover, the pillow is more readily damaged by changing the pillowcase.