All packaging must have some flexibility. This means that the package has to be made from plastic but not too rigid plastic, about 15% flexibility is ideal. Not all plastic is created equally too. PET is often the best as it will help minimize oxidation. Certain plant-based materials can be very porous causing oxidation.
The seals on the package are equally as important as the flexibility. For bottles, a plug cap is recommended over an induction seal. For containers with a flange, make sure the width of the flange is wide enough to provide a seal that will not break under the pressure. The width of the flange is often based on the size of the container. Typically a larger container will require a wider flange. The headspace in a container can also impact the necessary width of the flange. More headspace will require a wider flange and too much headspace can burst the seal. Regardless of the width of the seal, any seal for a container or package the contact surface must be clean. If food or especially oil (including meat fat in deli meat packages) can impact the quality of the adherence of the seal.
Packaging includes, but are not limited to:
1. Bottles
PET - Injection stretch blow molded for clear containers.
HDPE - Blowmolded for translucent to opaque containers.
PET bottles offer higher oxygen barrier than HDPE at common thicknesses.
PP - Commonly used as base material for closures, which can also incorporate thermoplastic elastomers (TPE) in some versions for tight seals.

Induction sealable liners principally comprise aluminum foil combined with a heat seal peelable layer of LDPE or copolymer-type materials. Head space can be flushed with N2 after filling to minimize oxygen in head space.
2. Tubs
Semi-rigid, sealed polymer container capable of use for paste, solid/sauce mixtures or liquid products. Typically labeled or decorated on sidewalls as well as on snap fit lids that cover film seals.
PET - clear or pigmented containers.
HDPE - translucent to opaque containers.
PP - good contact clarity containers.
Co-extruded structures can include EVOH or nylon for enhanced oxygen barrier; barrier lid films should be used in conjunction for high total package barrier.

Majority of containers are thermoformed, but injection molded versions also possible, and make incorporation of in-mold labeling (IML) technology for integral sidewall labels. Injection molding also permits greater control over container thickness profiles and can achieve higher height to width ratios with good thickness profile control.
Lid films range from oriented films with peel-seal layers to complex and heavy weight coextruded films.
Snap fit lids or over caps are generally PET or PP, although PE versions can be used; they typically are monolayer, do not provide barrier and are labeled or decorated; they can be clear or opaque depending on the appearance of the product or marketing considerations.
Heat sealed lids.

Can be gas flushed to limit oxygen in headspace and extend shelf life.
3. Flexible Pouches and Bags
Flexible, sealed polymer-based packages that can be used for liquid, paste or solid products. Used for retail and food-service/processor packs. Depending on channel, decoration ranges from sophisticated printed structures to post applied labels. Soft drinks, bottled waters, wines, spirits and specialized nutritionally enhanced beverages are also packaged in flexible packaging.
4. Trays
Semi-rigid, sealed polymer container capable of use for solid foods or ready meal components consumers either consume directly from the container or remove individual items for use in recipes or placement on a serving dish. Typically labeled or decorated on flat lid film surface unless secondary pack contains the tray. Can also be vacuum skin packed with drawn film covering product placed in tray.
5. Flexible packaging
Vacuum-packed and modified atmosphere packaging (MAP). A lot of meat products are packaged in flexible vacuum packed packaging.
6. Labels
Label should be waterproof. There are a few options: silk-screen printing directly on the bottle, a shrink sleeve, which can be applied before or after HPP, or a vinyl label with a rubber-based adhesive (no paper products, even if they're encased in or lined with plastic).
7. Bottle Caps
The most critical element of any bottle destined for HPP is its cap, the threads on the bottle neck and inside the cap and whether the cap has an inner seal. The threads need to be tight locking and completely married or there will be an increased risk for leakage upon decompression in the vessel. It is also preferred that the cap has an inner seal that lines up with the lip of the bottle when the cap is twisted on and that the cap cannot be over tightened. PET, HDPE & PETE plastics are the best with a double seal lid.

Smaller caps with one ring inside typically does not work as well. Double ring caps are ideal.
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