Sensors for the IoT (Internet of Things) society must be manufactured in large volumes with minimal environmental impact, achieving energy and material savings according to social initiatives, such as the global sustainability goals (SDGs), while ensuring high sensor performance and reliability. This presentation introduces various flexible, printable sensor technologies that utilize the resistance change of conductive composite layers of carbon-based and polymer-based host materials. Ecofriendly flexible humidity sensors with high sensing performance are desired for next-generation wearable electronics. We developed a fully printed high-performance flexible humidity sensor using all-carbon functional materials. The electrodes and sensor sensing layer were printed using all-carbon-based cellulose nanofiber/graphene nanoplatelet (CNF/GNP) composites. The features and benefits of these sensors are as follows: • Easy to fabricate by developing a new composite conductive material that is suitable for screen printing. • Manufacturing costs can be reduced by using carbon-based particles as a conductive material with printing processes. • Enables various resistive-type sensors that a simple circuit can drive, with high sensitivity and good reliability. Using CNF as the host material and GNP as the conductive material, a newly developed CNF/GNP ink can be prepared by simple mixing without any complex processes. Through an absorption and desorption mechanism, the developed humidity sensors showed a high resistive response of 120% over the relative humidity (RH) range of 30% to 90%, with response and recovery times of 17 and 22 s, respectively. We also developed a pressure sensor and stretchable strain sensor using polydimethylsiloxane (PDMS) from Dow Chemical Co. as the host material and carbon black from Lion Corporation as the conductive material. The developed pressure sensor showed a high resistivity change by applying pressure with a high sensitivity of 0.014kPa-1. The developed stretchable strain sensors were stretchable to 100% with small hysteresis, and a gauge factor of approximately 14 was obtained, demonstrating high sensitivity. As proof-of-concept, we demonstrated these sensors in human respiration detection, non-contact proximity sensing, and gripper control for robotics. We have been developing these sensors and their applications in collaboration with a major textile company and selected sensor device companies in Japan.