The Format Decision Comes Before the Machine

Three formats, three jobs

A sachet is not a sachet. The stick pack is for powders and granules dosed by the gram, easy to tear and pour. The 3-side seal is the workhorse for liquids and pastes — it leaves one open edge that becomes the fill throat, so the seal is never asked to hold product at the seam. The 4-side seal closes all four edges; it looks tidy but traps product at the fill edge unless the film and dwell are perfect. Choosing by appearance rather than by product is the most common upstream error.

Film structure is half the seal

The seal is only as good as the film's sealant layer. A PET/PE laminate seals on PE at 150–170 °C; a PET/ALU/PE needs 180–200 °C and a longer dwell, and a wrinkle in the aluminium kills it. The film is specified by the product's grease, acid, and oxygen need — not by price per square metre. A sauce sachet that bleeds grease through a cheap monolayer fails on the shelf, not on the line.

Why 4-side leaks on liquids

A liquid fills through one open edge. On a 3-side sachet, that edge is the top, and the three sealed sides never touch product. On a 4-side sachet, the fill edge must be sealed while wet unless the machine evacuates and cleans it first — most do not, so a film of sauce sits in the seam and the seal opens in the carton. For any liquid or paste above 1,000 cP, 3-side is the safe default; 4-side belongs to dry and free-flowing product.

Field case: sugar and ketchup, Casablanca, Morocco

The plant ran a 10 g ketchup sachet on a 4-side machine at 110 sachets/min, film PET/PE, in a 26 ± 3 °C room. Leakage ran 2.6% by retail audit, plus a 1.1% wrinkle reject from film misregistration.

We switched the ketchup to a 3-side format with a wider sealant layer (PET/PE, 70 µm, PE sealant 40 µm) and added an edge-wipe before the final seal; the sugar stayed on 4-side as it should. Leakage fell to 0.3%; the wrinkle reject dropped to 0.2% after tension tuning. Speed held at 110/min. No machine change — only format and film.

Where lines stall

1. Format chosen for looks. 4-side on a liquid leaks. Match format to product phase.
2. Film bought on price. A thin sealant layer wrinkles and leaks. Specify sealant thickness for your product.
3. No edge-wipe on wet product. Product in the seam opens it. Require an edge-wipe for liquids and pastes.
4. Misregistration waste. Poor film tension scrapes metres per hour. Tune tension and register at commissioning.
5. Multi-lane imbalance. On 6–10 lane stick lines, lanes drift; require per-lane weight checks, not a line average.

Meeting regional rules

European Union

Food contact under EU 10/2011; CE marking. For condiments, migration limits apply to the sealant layer — declare it. Average quantity rules reward tight dosing.

United States

FDA 21 CFR 110 for food contact; NIST Handbook 133 for net quantity. Ketchup and sauce fall under low-acid or acidified food process rules depending on pH.

Southeast Asia

Morocco sits at the edge of the EU-Mediterranean trade zone; for broader SEA (Thailand, Vietnam, Indonesia), halal covers the Muslim market and local food-contact rules apply. Heat accelerates grease bleed through weak film.

Middle East

Saudi SFDA and GCC anchor conformity; halal (SASO/GSO) mandatory. Shelf life in Gulf heat demands a proper oxygen and grease barrier in the film.

Specification & RFQ checklist

• Name the format (stick / 3-side / 4-side) from the product phase, not the catalogue photo.
• Specify the film structure and sealant thickness for your grease, acid, and oxygen need.
• Require an edge-wipe station for any liquid or paste.
• For multi-lane, require per-lane weight checks and balance reporting.
• For liquids, default to 3-side unless the machine proves 4-side wet sealing.
• Confirm CE / FDA / halal scope for your markets.

Questions buyers ask before signing

Stick or 3-side for my powder?

Stick for 1–30 g powders and granules poured into a cup; 3-side for the same if you want a wider face for print. Both seal reliably. 4-side is for dry condiment, not liquid.

Why does my ketchup sachet leak?

Almost always a 4-side format with product in the seam, or a film too thin at the sealant. Switch to 3-side with an edge-wipe and a thicker sealant; on the Casablanca case that took leakage from 2.6% to 0.3%.

Can one machine run all three formats?

With tool sets, yes — but each format is a swap and a validation. If you run one product, buy the format, not the flexibility.

How much leak is acceptable?

Well-set 3-side lines run 0.2–0.5%. Above 1% you will be audited out by the retailer. The format, not the machine speed, decides this.

Written by Helen Xu | Chief Industrial Application Engineer

Helen Xu is a Chief Industrial Application Engineer with 9 years of specialized experience in packaging machinery and liquid filling machine design, equipment model selection, and full production line process optimization. He focuses on delivering customized packaging & filling solutions for pharmaceutical, food, and chemical manufacturing industries, with mature practical expertise in GMP compliance, ISO 9001 quality management standards, and turnkey large-scale filling & packaging production line integration.