Corrugated plastic signs with wire stake is made of polypropylene (PP) corrugated plastic. 

Corrugated plastic or corriboard - also known under the tradenames of Polyflute,Coroplast, FlutePlast,IntePro,Proplex,Correx,Twinplast,Corriflute or Corflute - refers to a wide range of extruded twinwall plastic-sheet products produced from high-impact polypropylene resin with a similar make-up to corrugated fiberboard. It is a light-weight tough material which can easily be cut with a utility knife. Manufacturers typically offer a wide variety of colors http://www.cartonplastic.com