The degree to which the bands are inverted plays a crucial, firstorder role in determining whether bands are warped in a material. This is discussed in the context of rock-salt materials in Ref. 18 using a perturbation theory-based model of the band edges. Here, using a fully generalized model as described in Section 5.1, we find that bands become warped in all topological insulators when the bands are sufficiently inverted. We can arrive at this conclusion by noticing that the inequality in Eq. ( ) is satisfied when M0 is negative and large in magnitude, corresponding to highly inverted bands. The concept is illustrated in Figure , where the bands become warped only once the bands are sufficiently inverted and Eq. ( ) is satisfied. We explain in Section 2.2 why warping does not occur when the bands are normally ordered (M0 > 0).