Abstract: A wellbore isolation device, comprising: a mandrel 24 having a cylindrical body, a sealing element 38 disposed about the mandrel 24 and radially expandable from a first run-in diameter to sealing engagement with the an inner surface 50 of the wellbore 6; a metal backup ring 60 disposed on the mandrel 24 contacting one side of the sealing element system 38 with an initial height H and radially expandable and axially deformable to abut the inner surface 50 of the wellbore 6; wherein the metal backup ring 60 is a concave cross-section about the mandrel 24 with an uphole leg and a downhole leg; and wherein an applied compressive force expands the sealing element system 38 into sealing engagement with the wellbore 6 and the metal backup ring 60 radially expands while axially deforming to abut the inner surface 50 of the wellbore 6 with no contact pressure.