Flexible pressure sensor with excellent sensing performance and wearability is a major research focus for wearable electronic devices. In this study, polyporrole (PPy) wrapped cotton pads and silver coated wrinkle papers are stacked together to construct a novel piezoresistive sensor, and a bimaterial conductivity-conversion mechanism is presented. The PPy-cotton pads are prepared by an in-situ vapor growth process to ensure the strong adhesion and uniform distribution of PPy, which is beneficial for the stability of pressure sensors. The optimal flexible pressure sensor exhibits fast response speed (about 50 ms) and ultra-low detection limit (0.09 Pa). The potential applications of sensors as wearable e-skin for human activity and physiological signals monitoring are also demonstrated.