Thin, flexible metallic sheets or strips, commonly specified as being below a given thickness. Used widely as packaging materials — e.g. aluminium foils — which provide excellent barriers to moisture, oxygen, light and aroma, protecting food quality and extending shelf life. Foil gauges below about 0.15 mm suit lidding and wrapping, while thicker foil forms semi-rigid trays; pinholes are the critical defect, controlled by rolling practice and lamination to plastic films. Lacquering the food-contact side prevents corrosion from acidic foods, and embossing improves dead-fold properties for wrapping confectionery and cheese.