An editable poly is a type of deformable object. An editable poly is a polygonal mesh; that is, unlike an editable mesh, it uses more than three-sided polygons. Editable polys are useful in that they avoid invisible edges. For example, if you use a cut-and-slice operation with editable polys, 3ds Max doesn't insert extra vertices along any invisible edge. You can convert NURBS surfaces, editable meshes, splines, primitives, and patch surfaces to editable polys.