There are 2 zippers. One to open the bag, and another that zips around to expand the bag. When you zip the outside one, it collapses to very thin and is very snug on the passenger seat. The whole unit wraps around the passenger seat and is very snug (uses elastic and velcro under seat). Even zipped down to thinnest, I can still get 2 cell phones, and toll booth transponder in it. Opened up, you can get quite a bit of stuff in it.
2008 Hayabusa - traded for s1000rr