Straintronics (from strain and electronics) is the study of how folds and mechanically induced stresses in a layer of two-dimensional materials can change their electrical properties. [1] [2] [3] [4] [5] [6] [7] It is distinct from twistronics in that the latter involves changes in the angle between two layers of 2D material. However, in such multi-layers if strain is applied to only one layers, which is called heterostrain, strain can have similar effect as twist in changing electronic properties. [8] [9] It is also distinct from, but similar to, the piezoelectric effects which are created by bending, twisting, or squeezing of certain material.