<p>Accurately perceiving object softness remains challenging for tactile sensors, as current approaches estimate Young’s modulus from object deformation in response to an applied pressure while overlooking the pivotal role of Poisson’s ratio in shaping that deformation. Here we present a tactile sensor that quantitatively and accurately detects both Young’s modulus and Poisson’s ratio, achieved by constructing a broad materials library spanning diverse Young’s modulus–Poisson’s ratio and capturing materials’ surface bulging height–pressure trajectories. Using these trajectories as machine-learning features, our sensor achieved 84.7% anti-error rate assessment (ARA) in predicting Young’s modulus, markedly higher than 73.3% using pressure-bulging height pairs, and, for the first time, enabled quantitative inference of Poisson’s ratio with 87.7% ARA. Kendall’s Tau analysis verified a Young’s modulus ranking ARA of 91.3% for our sensor, outperforming conventional approaches (66.8%). The mechanistic influence of Poisson’s ratio on bulging morphology was revealed via a materials-library-enabled univariate experimental strategy combined with finite element simulations. When deployed on a robotic manipulator, the sensor generalizes to unseen samples, enabling accurate perception of Young’s modulus across diverse materials and heralding a new paradigm for next-generation tactile sensing.</p>