Plastic bags By Emma Mathieson and Maddy Bridge PLASTIC BAGS THE RAW MATERIAL Plastics are polymers, meaning they compose of essentially one molecule shape repeated continuously for a chain of molecules with the same atomic structure. A plastic bags raw material is usually crude oil or natural gas. How long does plastic bags stay in a landfill Scientists think that plastic bags break down between years. Of course no one has been around long enough to know but scientists have done tests and found out. The process of plastic bags Petroleum is heated to produce ethylene gas this is converted to polyethylene gas which looks likes porridge then it is forced through holes into strings which are cut into granules. These are heated stretched and cooked to make plastic bags.