Food Packaging Material Basics

Choosing materials for food packaging bags rests on a few basic points of common knowledge, which can be looked at from the angle of layer structure, the role of each layer, safety, and substitution trends.

Start with structure. By material structure, the inner layer is usually PE or CPP, the outer layer is PA or PET, and the middle layer may be EVOH or PVDC and the like; in some cases aluminised film or aluminium foil is used. The division of labour between the inner, middle and outer layers largely decides what the bag can hold and how long it can keep it.

On safety: compared with non-food packaging, PP and PE contain no plastic additives and will not release toxic substances during use, which is why they are so often the first choice when a food packaging material is selected.

Next, the role of each layer. PE and CPP have better heat-sealing properties, which means they seal easily. PA and PET print better, so they are used on the outside, where attractive graphics can be printed. PVDC and EVOH have better barrier properties and prevent oxidation. Aluminised film and aluminium foil block light well, which suits products that should not be exposed to light.

In PVC packaging, almost all cling film used to be made of PVC, but because of its safety issues it is now gradually being replaced by PE cling film.

Finally, the difference between PE and PP. Bags made of PE are softer, and their mechanical properties are weaker than those of PP; typical products include supermarket shopping bags, cling film and rubbish bags. PP is harder and anisotropic — a small notch makes it easy to tear — with good mechanical properties and better high-temperature performance than PE. Typical examples are bread bags, fruit bags, and structures such as E/Al/PE and Al/PE. Comparing PE with PP side by side makes it easier to see why soft bags and rigid bags tend to be built on different base materials.