With the use of our Air Bed Components, our exclusive 1.8 lb. Density, rail design, prevents the bed from bowing out on the sides. Other manufacturers' rails use Velcro at the corners or with Sleep Number™, only lock in the corner (think "Lincoln Logs") or sit in 4 inexpensive, plastic elbows, that are placed in the corners, inside the bed. Both our head and foot rails are connected as are our 2 side rails connected, with a thin layer of, non stretchable, nylon cloth forming a box inside of our air beds. Our "Perimeter Support, Sling Rail Design" will not allow the air chambers to bulge out and keeps the air chambers tight, so there is no "Gap" or "Hole" down the middle of our Air Beds. There is NO NEED FOR A CENTER FOAM "WALL" INSERT. Our "Perimeter Support, Sling Rail" System also helps to prevent "The Hammock Effect" (where your head and feet are higher that the middle part of your body), gives our customers a much better edge to sit on, that does not "Sag Out" when sat on and makes assembly much easier! Again, this "Perimeter Support" rail system is designed for the specialized components offered in our Air Beds and may not supply the above, described results, with other Air Bed Components. If you have questions, please give us a call!