Author(s): Huang Lu and Zhaohe Dai Indentation is one of the simplest ways to feel the stiffness of matter. Interpreting indentation, however, requires care, especially for thin films—such as biological cells or soft coatings supported by rigid substrates—because the substrate effect can make a film appear orders of magnitude stiffer… [Phys. Rev. Lett. 137, 036201] Published Tue Jul 14, 2026