How To Prevent Paneling

Have you ever picked up a bottle of lotion and found that the side-walls had caved in. Or perhaps, you have had the unpleasant experience of a plastic bottle bursting inside your luggage after an airline flight? Both of these situations are the result of a difference in pressure between the inside of the bottle and the outside environment. In the container packaging industry, the inward distortion of a containers side-walls as a result of these differences in pressure is referred to as “Paneling”.

What is Paneling? - Paneling occurs when the pressure inside a plastic bottle achieves a negative level to that of the air pressure outside of the bottle. When this happens, the walls of the plastic bottle begin to collapse inward.
Paneling normally won’t harm the contents within the bottle. However, a bottle that has paneled is structurally compromised, may leak around the closure, and can cause the label to become loose and peel off. Ultimately paneling is unsightly, and fosters distrust from customers.

bloated bottle-normal bottle-paneled bottle


Why Does Paneling Happen? - There are a number of things that can cause a plastic bottle to panel. The most common causes are hot filling, chemical reactions, changes in altitude, or poor packaging and storage practices. It’s important to understand that ALL paneling issues are a result of a negative difference in the air pressure between the inside and outside environment of the bottle or container. Normally, this isn’t a problem. Most bottles are designed to compensate for minor pressure changes, but sometimes, when the interior pressure becomes too extreme, paneling or bloating occurs. Let’s take a look at some of the most common causes of plastic bottle paneling..

Chemical Reactions - A chemical reaction, such as “oxygen absorption” happens when a product like citrus cleaning formulas, industrial cleaners, essential oils and automotive products consume, or “scavenge” oxygen molecules from the inside of the bottle. Causing a negative pressure which pulls the walls of the bottle inward.  Alternatively, organic products and agrochemicals, can off-gas, increasing the internal pressure of a container and causing it to bloat.

Changes in Altitude - Any packaged product that is filled at a higher elevation and shipped to a lower elevation is at risk of paneling.  The opposite can also be an issue of the bottle bloating.  The extreme differences in elevation and therefore, air pressure, found in air transportation has the potential to cause paneling.

Hot Filling - Heated air expands and INCREASES pressure. As it cools, it contracts, and DECREASES pressure. Air pressure and contents inside a bottle having COOLED and CONTRACTED, causes a negative pressure inside the bottle. Remember, it’s all about the internal pressure achieving a negative level to that of outside. This happens when a product cools, the molecules within the bottle contract, creating negative pressure, which can lead to paneling.
Many sauces are “hot-filled” into the bottle and then allowed to cool. However, capping the bottle too soon, before the product has had the time needed to cool, can cause paneling.

How To Prevent Paneling? - There are several effective methods used to prevent paneling. The three most common solutions are 1) Fluorination, 2) Using a Vented Liner, and 3) Adding More Plastic to the walls of the container or bottle.

Fluorination - Is a process that exposes the surfaces of a plastic bottle or container to fluorine ions through carefully controlled temperature, time and pressure. The hydrogen atoms on both sides of the bottle or container are replaced with fluorine atoms that also bind to the plastic, sealing it. This creates a permanent, chemical resistant, non-permeable barrier that seals both sides, and prevents solvent and chemical permeation.

There are several Fluorination levels that can be applied. Based on needs of the customer. It can be applied to all polyethylene and polypropylene plastics.

Fluorination is FDA safe, recyclable, permanent and effective, but the process can be expensive.

Fluorination process illustration


Vented Liners - Another solution is to regulate breathability via the cap and cap liner. This is the simplest, most cost-effective solution to overcome any temperature, chemical, or altitude pressure situation. Breathability stops container paneling by allowing the inside and outside pressures to equalize.
Vented Liners are an ideal way to accomplish this task. They allow gas and moisture to pass through to help equalize the difference in pressure between the inside and outside of the container. This is done by allowing the right amount of airflow and pressure to release from within the plastic container or bottle through the liner itself. The venting can be a membrane portion of the liner or it can be a mesh portion of the liner. At times even a hole in the cap might be necessary.  Vented liners are designed to allow your product to “breathe”, regulating the pressure within the bottle or container while keeping contaminants out and preventing liquid leaks.

vented liner illustration
Heavier Bottle - A common solution to the paneling problem is to add more weight to the bottle. The added material can resist the inward pressure. There may be manufacturing minimums that are required for this option. A sales rep can help answer any questions regarding this options. 

Other Options - Some paneling can be prevented by letting a hot-fill product cool to ambient temperature before capping the bottle. Increasing the fill level of the product limits the amount of air-space within the bottle. It can also be inhibited by purging the leftover headspace in the bottle with a neutral gas like nitrogen to eliminate the oxygen before applying the cap.

Test Your Products and Packaging - Here at Aaron Packaging Inc, we want you to succeed. We advise that you request samples of the packaging products you plan to use. And perform tests with your product for compatibility and to ensure that you have prevented paneling before you place any large orders.

Questions? Contact Our Sales Team! - If you are struggling with your containers showing paneling. Give us a call! Our support team will help you with advice and finding a dependable solution to your problem.  Please contact our  customer service team

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