You are correct it will compress slightly over time (even 1 night) . But its just beanbag /packing material and pretty darn cheap. The pantyhose works great too and is super easy to make, just cut and tie it off. If you are ?fortunate?! enough to have a wife that is an super xl queen size, that could be free too. Pantyhose material is fairly strong, almost weightless, and stretchy.
I used it one night, found it worlds better than raingear in sack. Conforms exactly to head, holds head in position, warm, firm, but not hard under head, and much more comfortable than raingear in the hyperlight mountain pillow I have.(1.2 oz)
Agreed if you dont have room, you do something else. Its a bit bulky.