Corrugated plastic

From Freepedia

Corrugated plastic also known as Corriflute or Coroplast is plastic sheeting with a similar make up to corrugated cardboard. It is a light weight tough material which can easily be cut with a craft knife.

This material is commonly used to create commercial signs. It has recently found a use among guinea pig and other small pet enthusiasts as a component of a type of DIY cages popularized on http://www.cavycages.com.