Force Sensing Resistors are among the oldest printed electronic components )invented in the 1980's by Franklin Eventoff) and for sure the mostly used force sensing concept as it fulfills our keyboards and many other touch key devices.
They can be found at standard shape and sizes from industrial manufacturers (Sensitronics, Interlink, Tekscan) or they can be house-made using resistive plastics or textiles and metal or metalised electrodes but here we like to build them from a combination of paper with metal-free electrodes and a highly sustainable finished product.
Check out these fabrications guides and other related resources to build any force sensor of any size and shape with a full control over the sensor response, its conditionning and its recyclability,