The whole frame with foiled plates for EMF interference blocking from any noise that may backfeed through the power wires or power supplies. 14.4 ounces, that is at least 2.4 ounces lighter than the OEM F550 frame and the arms have a dihedral angle and also two motor mounts per arm. This equals more performance features less weight. Being slightly lighter should hopefully translate to a slightly lower hovering power requirement as well.