A one-piece co-formed exterior hard shell case with an elastomeric liner formed on the interior of the exterior hard shell for mobile electronic devices. This hard protective exterior shell allows the device maximum protection from impacts with sharp objects while the interior elastomeric portion that provides shock protection for the device from impacts. The exterior hard shell part is formed to fit the device closely with a small offset from the devices surface. The exterior hard shell raps around the edges of the device. To allow the shell to be able to be mounted on the device the corners of the hard shell are cut open. This allows each sidewall to flex away when a device is inserted and snap back once it is in place. The elastomeric material fills in the gaps created at the corners of the exterior hard shell to allow flex for mounting.