A backup ring design for a packer sealing element features a folding shape where opposed legs are pushed together for extension in a radial direction toward the surrounding tubular to span the extrusion gap. The design can use a V-shape where the vertex is toward the mandrel and the legs are oriented toward the surrounding tubular. The legs in that instance can be thicker than the vertex thickness to aid in folding while providing enhanced strength at the surrounding tubular where shear forces apply as a result of seal compression against the surrounding tubular. The design features a single or multiple vertices that are similarly aligned or alternatingly oppositely aligned to create a zigzag shape in cross-section. Material selection can vary with the expected service conditions.