FOOD PACKAGING: PACKAGING MATERIALS
Diagram
Flexible and rigid packaging: bending packs and holding shape packs
Flexible packaging
Films, pouches and bags that bend and fold. The pack takes the shape of the food, and it is flat when empty.
↓
Rigid packaging
Bottles, cans, jars and tubs that hold their shape whether full or empty. The pack keeps its own form.
↓
The choice
Flexible suits light, space saving packs. Rigid suits foods that need protection from crushing and a pack that stands on a shelf.
Figure 1: Packs that bend compared with packs that hold their shape. Drawn in our own style from Lee, Yam and Piergiovanni, Food Packaging Science and Technology, CRC Press, and Robertson, Food Packaging: Principles and Practice, 2nd ed., CRC Press, 2005. Note: the comparison is drawn from the polymer, glass and metal chapters, not from a single head to head passage.
Introduction
Flexible packaging and rigid packaging are the two forms of food packs, divided by whether the pack bends or holds its shape. Flexible packaging is made of films and foils that bend and fold: pouches, bags and wraps that take the shape of the food and lie flat when empty. Rigid packaging is made of glass, metal or thick plastic: bottles, cans, jars and tubs that keep their own shape whether they are full or empty.
The core difference is form: flexible packs adapt to the food, while rigid packs keep the food in a fixed shape. Flexible packs save space and material, while rigid packs protect the food from crushing and stand upright on a shelf.
Quick comparison
Table 1: Flexible packaging compared with rigid packaging
| Aspect | Flexible packaging | Rigid packaging |
|---|---|---|
| Form | Bends and folds, takes the shape of the food | Holds its shape, full or empty |
| Examples | Pouches, bags, wraps, sachets | Bottles, cans, jars, tubs, trays |
| Materials | Plastic films, foil, paper laminates | Glass, metal, thick plastic |
| Weight | Very light | Heavier |
| Space when empty | Flat, takes little space | Full volume, takes the same space empty |
| Protection from crushing | Low, the food can be squashed | High, the pack shields the food |
| Stands on a shelf | May need a stand or a display | Stands upright on its own |
| Barrier | Depends on the film layers used | High in general, especially glass and metal |
| Cost of material | Low per pack | Higher per pack |
| Food example | Snack pouch, coffee pouch, soup pouch | Jam jar, drinks can, yogurt tub |
Scientific explanation
Definition
Flexible packaging is packaging made of flexible materials, such as films, that can be bent and folded. Rigid packaging is packaging made of rigid materials that keep their shape and protect the contents from crushing.
Working principle
A flexible pack protects food through its film layers: each layer adds barrier, strength or sealing, and the pack is sealed around the food so little air is left inside. A rigid pack protects food through its shape: the walls are strong enough to take stacking and handling without bending, and the lid or cap seals the opening. Both kinds must seal well, because a poor seal lets air and moisture in whatever the form.
Apparatus
Flexible packs are made on form fill seal machines, which form a pouch from a roll of film, fill it and seal it. Rigid packs are made by blow moulding, injection moulding or thermoforming for plastic, and by glass forming or can making for glass and metal.
Measurement procedure
The books name no single standard test that compares the two forms. In practice the seal is checked for leaks, the pack is checked for how much gas passes through it, and filled packs are dropped and stacked to check whether they protect the food.
Factors affecting readings
For flexible packs, the result depends on the film layers, the thickness, and the quality of the seal. For rigid packs, the result depends on the wall thickness, the material, and the closure. Rough handling harms a flexible pack more than a rigid pack, because the flexible pack has no shape to protect the food.
Formulas and calculations
The books read give no formula for flexible against rigid packaging. The comparison is made from form and material: flexible packs are judged by film barrier and seal strength, and rigid packs are judged by wall strength and closure. No formula is given here.
Industrial applications
- Flexible packaging: snack pouches and coffee pouches, where a light, space saving pack suits a dry food.
- Flexible packaging: soup and sauce pouches, where a pouch takes little space in transport.
- Flexible packaging: sachets and single serve packs, where a small film pack suits one portion.
- Rigid packaging: jam jars and sauce bottles, where the pack must stand on a shelf and protect the food.
- Rigid packaging: drinks cans and yogurt tubs, where a pack that holds its shape suits filling and stacking.
Advantages and limitations
- Flexible packaging, advantage: light and space saving, with low material use and low transport cost.
- Flexible packaging, limitation: poor protection from crushing, and a pack that does not stand on its own.
- Rigid packaging, advantage: strong protection from crushing and a pack that stands upright and stacks well.
- Rigid packaging, limitation: heavier and bulkier, with more material per pack and more space when empty.
FAQ
Is a pouch flexible packaging?
Yes. A pouch is made of film that bends, so it is flexible packaging.
Is a yogurt tub rigid packaging?
Yes. A tub holds its shape whether full or empty, so it is rigid packaging.
Which is better for the environment?
That depends on the material and the weight, and the books read do not settle it with one answer. Flexible packs use less material per pack, while rigid packs are often easier to recycle by type.
Why are soups sold in pouches now?
Because a pouch is light, takes little space, and can be heated in the pouch, while a can is heavier and bulkier.
Can flexible packaging protect food well?
Yes, if the film layers give a good barrier and the seal is sound. Its weak point is crushing, not barrier.
References and further reading
- Fellows, P., Food Processing Technology: Principles and Practice, Woodhead Publishing (FTN book on disk).
- Lee, D. S., Yam, K. L. and Piergiovanni, L., Food Packaging Science and Technology, CRC Press (Google Books page read: Ch. 6, Polymers, flexible films, and Ch. 7, Glass, rigid containers).
- Robertson, G. L., Food Packaging: Principles and Practice, 2nd ed., CRC Press, 2005 (Google Books page read: paper, metal, glass and polymer material chapters).
