Basically filled with pillow stuffing. Worked to dampen. My brother uses one that is a series of water filled tubes. No movement between them. I now use a foam temperapedic ripoff.
While they were doing that I walked over to a place called the Oyster Bar - a real dive. But I knew the owner; he used to play for the Dolphins. I said, "HI GILL!" (You have to yell; he's hard of herring...)
47 ms