Abstract: A method of producing porous ionic conducting material, comprising the step of positioning an ionic substance into cellulosic material to form a continuous web or at least one individual sheet of porous ionic cellulosic based material, comprising the steps of first producing a web or sheet shaped cellulosic based substrate and thereafter applying liquid comprising room temperature ionic liquids. The porous ionic conducting material is used in flexible electronic device, by using the material as a substrate and applying a conducting material. A sensor assembly for sensing a property of an object, comprising at least one sensor wherein said sensor assembly comprises a flexible web or sheet shaped material. An authentication device for verifying the authenticity of an object. The device comprising at least one flexible electronic device.