a conventional exterior rear - view mirror is broken into vertical segments and collapsed into a stack in a plane roughly orthogonal to its original plane , so the frontal area is drastically reduced , thereby reducing drag and increasing fuel mileage . the total projected width of the vehicle is also reduced . in one embodiment of the invention , the exterior rear - view mirror is formed as part of a side window , thereby completely eliminating projections to achieve advanced streamlining , and also potentially decreasing manufacturing costs . in another embodiment , a rear view is provided from a sun roof . when formed as part of the canopy of an aircraft , a rear view is provided without significant weight or complexity . another embodiment of the invention lies in a sheet of flexible adhesive - backed plastic which may be affixed to a window . in the context of a truck , the exterior rear - view mirror does not project significantly beyond the innermost edge of an equivalent conventional rear - view mirror , thereby reducing both drag and excess lateral dimension .