Supporting information for: Unraveling the Elastic Properties of (quasi)2D Hybrid Perovskites: A Joint Experimental and Theoretical Study Marcos A. Reyes-Martinez, †,‖ Peng Tan, ‡,¶,‖ Arvin Kakekhani, ‡,‖ Sayan Banerjee, ‡ Ayan A. Zhumekenov, § Wei Peng, § Osman M. Bakr, § Andrew M. Rappe, ∗,‡ and Yueh-Lin Loo ∗,† †Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544-5263, United States ‡Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323, United States ¶Department of Physics, Harbin Institute of Technology, Harbin 150001, China §Physical Science and Engineering Division, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia ‖Contributed equally to this work E-mail: rappe@sas.upenn.edu; lloo@princeton.edu S1