[lettie]

The greaseproof paper covers the top of the tray here, once the chips are in it. If your chips are being wrapped instead of in a tray there will also be greaseproof paper in the wrapping. This stops the grease and vinegar from the chips leaking into the surrounding paper after wrapping. That way your chips will stay wrapped and intact until you get home and open them. I don't know why they put cellophane on the bottom of the trays, my only suggestion is that they may be using cheap trays which absorb the fat and vinegar and would deteriorate mid-meal. We don't line the trays with anything here, our greaseproof paper goes on the top.