packaging material of potato chips

The common packaging material used for potato chips is aluminium coated polyethylene terephthalate (PET).
http://www.wipo.int/pctdb/en/wo.jsp?IA=WO2005076918&DISPLAY=DESC

As potato chips are sensitive to air as oxygen in air can cause racidity. Therefore the material need to have oxygen-barrier properties.
Aluminium coated packaging can prevent sunlight from entering which thus prevents rancidity too.