a stripper of the invention uses flat metal springs preferably made of spring steel and a flexible polymer based friction material covering the springs on one side so that the friction material contacts an incoming mail piece passing by the stripper along the friction surface presented by the outside of the friction material . a stripper according to the invention has variable stiffness , is quick responding , and is critically damped , meaning that incoming mail pieces will not bounce off it with excessive force likely to cause a misfeed or loss of control of the mail piece .