The 3 Real Boundaries of Metrological Assurance for Prepackaged Goods—Net Content, Negative Deviation, and Absolute Value: Where Printers Most Often Go Wrong on “500g × 24 Bags” Orders

One winter, a nut customer approached us to print composite flexible pouches for a 500g × 24 bags order. The specification sheet he gave us was beautifully written: net content 500g, tolerance ±3%, aluminum foil laminate. None of the earlier clauses required discussion. The only issue was the small text in the final line—“Must comply with the JJF 1070 requirements for metrological assurance of net content in prepackaged goods.”

What the customer meant was this: He wanted to place the product on supermarket shelves, where inspectors would randomly select 3 bags and weigh them on a net-content tester. Any bag below 485g would be deemed nonconforming, and the entire batch would be returned.

The reality on the packaging side was that the filling line for the composite pouches was located at the customer’s factory, not ours. We could control only one thing: how much the bag could hold. In other words, the bag’snet-weight capacity.

The First Boundary: Is the Printer Responsible for Net Content?

Most purchasing managers believe that “net content is a filling issue and has nothing to do with the printer.” That is only half true. The filling line determines the net-content value, butwhether the bag can accommodate that value must be established during printing and plate-making.

We once received an interesting project: A customer changed from a 60g bag to a 75g bag because “the unit price of nuts went up, so putting more in would make the product look better value.” The net content on the specification sheet changed from 60g to 75g, but the bag dimensions remained unchanged. The customer assumed that the bag would “stretch anyway.”

During sample production, however, the width of the filling opening did not match the width of the bag’s heat-sealing area. The volume of 75g nuts was approximately 30% greater than that of 60g. The filling opening was forced open, leaving only 6mm of heat-sealing area, which produced weak seals. The customer filled 200 bags for testing, and 11 bags ruptured.

Our conclusion to the customer was direct: The bag could not accommodate 75g. The customer either had to change the bag design, with a new plate charge, or increase the bag material from 60 μm to 75 μm, adding 0.12 yuan per 1,000 bags. The customer chose to change the bag design.

The boundary is this: The brand owner is responsible for the net-content value, but the printer must submit a written objection during plate-making if the bag cannot accommodate that value. If the printer raises no objection, the printer becomes the primary party responsible when a problem occurs, because the printer produced the packaging and had the ability to identify the issue during sampling.

The Second Boundary: Negative Deviation and the Average Value Are Different

This is the concept most easily confused by non-specialists and the one we most frequently explain to customers.

Suppose the customer requires 500g of nuts. Negative deviation means that no individual bag may be below 485g, for example, under a tolerance of -3%. Average value means that the total weight of all bags in the batch, divided by the number of bags, must not fall below 500g.

The logic of JJF 1070 is that the average must be sufficiently high, while a limited negative deviation may be allowed on individual bags, provided it never exceeds the specified limit. Both requirements must be satisfied.

On one occasion, a customer told us, “Our filling line is set to 490g, and our inspections have always passed.” We asked how the inspections were conducted. He replied, “Our quality inspector takes 3 bags, weighs them, sees that they are all above 485, and releases them.”

This is a typical failure mode. The fact that all 3 bags are acceptable does not mean that the batch average is acceptable. Supermarkets and third-party inspectors use a GB/T random-number table to select samples. They inspect 8 bags and calculate the average. If the customer’s filling line runs 10g low overall, increasing the bag’s net capacity is of no use. If the filling line is low, the extra bag capacity serves no purpose.

Our reminder to the customer was this: “Your specification sheet states the negative deviation, while we design the bag according to average capacity. Please provide the average-capacity value, because it is more important than the negative-deviation value.”

The Third Boundary: Absolute Content Error Versus Relative Content Error

This distinction is specific to goods sold by weight and does not apply in the same way to goods sold by count.

For products sold by count, such as “10 pieces,” the error is discrete: 9 pieces is nonconforming, with no intermediate state. Goods sold by weight are continuous: 499g and 500g differ by only 0.2%, but under strict prepackaged-product requirements, that difference can be measured.

Accordingly, JJF 1070 places an absolute-value constraint on average net content. For example, if the nominal content is 500g, the average may not be lower than 500g minus a specified absolute amount, nor may it exceed the corresponding upper limit. This also prevents the practice of “overfilling” to deceive consumers. It is a strict constraint on the filling line.

When designing bags, we encounter a practical problem: Customers often provide a bag designed for “maximum capacity,” such as a bag capable of holding 520g. This prevents rupture if the filling line overfills the bags. However, this design has 2 consequences:

First, the bottom and sides of the bag may appear empty, which customers may perceive visually as making the package look less substantial. Second, the bag’s visible front-printing area is reduced, compressing the high-resolution graphics area required by the customer.

We usually provide customers with 2 options: a bag designed for “nominal capacity +2%” and a bag designed for “nominal capacity +8%.” This allows the customer to choose between cost and fault tolerance rather than making the decision on the customer’s behalf.

An Account We Calculated Incorrectly

Last year, a customer asked for 2kg laundry-detergent bags. During plate-making, we designed the bag for 2.05kg on the grounds that this would “leave 2.5% filling tolerance.” The customer raised no objection and approved production.

During the 3rd production batch, the customer’s filling-line weighing sensor drifted, resulting in an actual fill weight of 1.94kg per bag. By the time the issue was discovered through sampling, 8000 bags had already been produced.

When holding the customer accountable, he said, “The bag could not hold enough, so the product was underfilled.” We produced the plate-making confirmation sheet from that time, which recorded the 2.05kg net-capacity parameter approved by the customer’s signature. Responsibility lay with the filling line, not the bag. Nevertheless, the dispute continued for 2 weeks.

Afterward, we changed our procedure: On every plate-making confirmation sheet, the 3 fields related to net content—nominal value, average-capacity design value, and negative-deviation limit—must appear on a separate line, immediately adjacent to the customer’s signature field. Otherwise, what the customer signs is what the bag looks like, not how much it can hold.

3 Things a Printer Can Actually Do

First, include the bag’s net-capacity parameters on the quotation during the quotation stage. Do not put them only on the design confirmation sheet, because customers generally do not review that document carefully.

Second, whenever the customer changes the nominal net content, proactively review the capacity of the bag design and retain the review conclusion in writing. This step takes less than 10 minutes but prevents most subsequent disputes.

Third, require the customer to provide a filled sample during the sampling stage, rather than examining only an empty bag. An empty bag does not reveal changes in shape after filling or problems caused by the heat-sealing area being forced open.

None of these 3 actions requires an additional charge, but each can significantly change the printer’s position in the chain of responsibility.

Further Reading

This article concerns the intersection of metrology and packaging standards. If you are dealing with other compliance issues, you may also want to read the following articles:

• Real Data on 6 Methods of Packaging Testing—Net content is only one inspection item; compression resistance, drop testing, and stacking each have their own acceptance criteria.
• A Quick Reference to 5 Types of GB/T Standards for Packaging Printing—First determine which standard governs the packaging itself and which governs sampling and acceptance.
• Practical Application of 4 Types of Packaging-Printing Quality Inspection Standards—On-site methods for determining color difference, registration, varnish, and peel strength.
• 5 Hidden Pitfalls in Gift-Box Quotations—Why net-content parameters must appear on the quotation rather than only on the confirmation sheet.