Flat panel pieces are backed with 3/4" interior Plywood which floats the piece off the wall. Each piece usually comes with a pair of matching cleat hangers, one being already attached and the other for your wall. You have the option of adding a security hanger system.
My signature sculptural pieces are constructed entirely from metal with a bronze angle structural framework that allows for a curved surface background and floats the piece off the wall 1 - 3" depending upon the size of the artwork. The above image shows the frame being soldered to a very large (five foot) piece for a curved rock wall so both the surface and the frame had to be different curves. The curve of this structural framework then had to match a second sub-frame hanger attached to the wall.
The image above shows both a three-dimensional element (in this case the bird, branch and leaves) and what I call "layering"; the metal being stacked or layered with varying thicknesses of plywood risers to achieve a sense of depth. Three-dimensional elements can be added to either flat panel designs or sculptural pieces. Layering on Sculptural pieces requires small metal frames.