Cushion.com makes cushions in two different types of constructions. Boxed Edge cushions and Waterfall Edge (or Knife Edge) cushions.
Boxed edge cushions are constructed with top and bottom fabric panels that are connected by an additional strip of fabric between the two panels, making the cushion look more boxed with well defined edges due to the double seams.
Waterfall edge cushions and knife edge cushions are constructed with top and bottom fabric panels that are sewn directly to each other, creating a softer, smoother edge resembling a waterfall when filled. Thinner cushions with waterfall edge construction are also commonly known as Knife Edge cushions.