Food Products must stay fresh until they are consumed. Water vapor often must be kept away from food, but sometimes moisture needs to be kept inside of a package in order to maintain freshness. In either case, a food package must have a low water vapor transmission rate (WVTR).
Other foods are sensitive to oxygen. Most often oxygen needs to be kept out of a package. In this case a package must have a low oxygen transmission rate (OTR). In some cases, minimizing food contact with oxygen is so important that replacing most of the oxygen with an inert gas is necessary.