Yes, the j pouch is a true pouch. It is hollow inside. When your small intestine was looped to form a "J" an instrument was inserted into the "cut end" (the bottom of the loop that is sewn to your anus). The instrument looks like a long staple gun and it staples your loop together permanently. While stapling, this same instrument also cuts the piece of middle tissue so that your loop is now a hollow pouch. I asked my surgeon, he said it is definitely hollow, and he drew a picture for me. There is also a YouTube video of an actual surgery removing the colon (for real) and constructing the j pouch, showing the staple gun making the cut. You need a strong stomach to watch.