How to Measure Sealing Integrity of Cosmetic Spout Pouch Sachets

Cosmetic spout pouch sachets usually hold serums, lotions and cleansers built on formulations that dislike air and moisture. Once the seal is compromised, leakage, oxidation and microbial growth follow, and the customer ends up holding a leaking or spoiled unit. As a supplier of spout pouches and liquid packaging bags, KODY PACK treats sealing integrity testing as a routine production step. The methods below range from fast on-line screening to precise laboratory checks, and together they answer one question: will this sachet actually hold?

Why sealing integrity defines the quality of a spout pouch sachet

• Cosmetic formulas are vulnerable to air, moisture and contaminants, and the seal is the only physical barrier between the fill and the outside.
• The failure chain is short: leakage leads to oxidation, oxidation opens the door to microbial growth, and product safety suffers.
• A consumer who receives a leaking or spoiled flexible package remembers the brand, not just the sachet.
• Holding a tight seal is therefore a baseline requirement for every sachet that leaves the factory, not a bonus feature.

Visual inspection and the bubble test: fast on-line screening

Visual inspection is the simplest option and can run directly on the production line:

• Seal appearance: you want a uniform, continuous seal; gaps, holes, wrinkles or lifting edges are warning signs.
• Seal width: measure it. A steady width suggests the sealing parameters are under control, while a width that drifts points to unstable temperature, pressure or dwell time.
• Product leakage: check around the seal area for any sign of product escaping; even a trace deserves investigation.

Keep in mind that visual inspection only catches obvious defects and is weak at spotting micro-leaks or weak seals.

The bubble test goes a step further:

• Prepare a container: fill it with water and optionally add a little soap to lower surface tension so bubbles are easier to see.
• Submerge the sachet: press it gently under the water to release trapped air.
• Watch for bubbles: bubbles rising from the seal area mean a leak, and their size and frequency hint at how severe it is.

The bubble test is quick and cheap, but its sensitivity is limited and very small leaks may go unnoticed.

Vacuum decay and ultrasonic testing: sensitive, non-destructive methods

A vacuum decay test measures the rate at which air leaks by creating a vacuum around the sachet:

• Place the sachet inside a sealed chamber.
• Pull a vacuum with a pump; chamber pressure drops and the sachet expands slightly.
• Monitor the pressure over time. If the sachet leaks, air enters the chamber and pressure climbs, and the rate of that rise tracks the size of the leak.

The method is highly sensitive, catches very small leaks, and is non-destructive, so the tested sachet can still be used.

Ultrasonic testing is non-destructive as well, sending high-frequency waves through the sachet and reading the reflections:

• An ultrasonic transducer transmits waves through the sachet.
• The waves reflect off the different layers, including the seal; analysing those reflections reveals gaps or weak areas.

It is fast and accurate and detects both surface and internal seal defects, but it calls for specialised equipment and trained operators.

Dye penetration and the case for scheduled testing

The dye penetration test is destructive:

• Mix a water-soluble dye with water to make the solution.
• Apply the solution to the seal area of the sachet.
• Let it sit for a few minutes so it can work into any leak path.
• Wipe off the excess dye and inspect: if the seal leaks, the dye penetrates and shows up on the inside of the sachet.

It is simple and effective, but the sachet cannot be used afterwards.

No single test proves anything on its own. Seal quality shifts with equipment condition, material batches and workshop temperature and humidity, so testing has to be a scheduled routine with traceable records. Only then do you spot a trend before it becomes a batch of returns.

If you are sourcing cosmetic spout pouch sachets, liquid packaging bags or bag-in-box pouches and want a supplier with a disciplined sealing and testing routine, contact Guangdong KODY Packaging. We supply spout pouches, bag-in-box (BIB), stand-up pouches with taps, colostrum bags, liquid packaging bags and laminated roll film, and we can provide samples and support seal strength and sealing integrity validation.