Like salty snacks, moisture barrier is a key requirement. A moisture vapor transmission rate (MVTR) of 0.1 to 0.4 g-mil/100 in2-day is usually needed. For products with high fat content, oxygen barrier is also needed to avoid rancidity, and films with the necessary moisture barrier usually have an adequate oxygen barrier as well. Multilayer films meet these requirements.
For crackers packaged in boxes, HDPE/EVA or OPP/E-P copolymer films are typically used as the inner wrap. Laminations and co-extrusions are used for box overwraps or bagged products, wherein OPP is used as the primary element.
On the other hand, PVDC, nylon, and EVOH impart the requisite barrier whereas ionomer, LDPE, or EVA provide the seal layer. Aluminium foil and paper are used frequently in plastic-based laminations. In particular, aluminium foil is used for attaining the ultimate feature in oxygen, moisture and freshness that enable soft cookies to have a fresh baked flavour.