Foldable substrates have a first portion, a second portion, and a central portion positioned therebetween. The first portion and the second portion have a substrate thickness less than a central thickness of the central portion. A plurality of protrusions extend from a first central surface area of the central portion. A total protrusion area is a sum of an area of an upper surface of each protrusion of the plurality of protrusions. A total central area is an area of the central portion. An area ratio of the total protrusion area to the total central area is from 0.10 to 0.70. Methods include disposing a patterned mask on an initial major surface of a foldable substrate and then etching the foldable substrate to form the plurality of protrusions.