Conductive sheets consisting of copper fibers,urea formaldehyde resins and decorative papers were prepared by hot pressing.The results showed that the sheet resistance of composites had mutations with the increasing of copper fiber filling ratio.The sheets exhibited percolation threshold effect.The threshold of sheets filled with 5 mm copper fibers was about 16% and the threshold of sheets filled with 10 mm or 15 mm copper fibers were about 8.7%.Meanwhile,the sheets showed piezoresistive characteristics and the conductive structure of sheets have been gradually developped into "three-dimensional conductive network" from "two-dimensional conductive network".Moreover,the length of copper fibers showed strong effects to the conductivity.Under the same fiber filling ratio,the larger length of fiber was,the higher conductivity and the lower percolation threshold could be.
