Air returning after freezing

Slow leaks usually start from tiny pinholes or a weak seal. Films become stiffer at low temperatures, and repeated flexing at the folds during boxing and transport can create pinholes. A bag that held vacuum at room temperature can still lose it in the cold chain. A polyamide (PA) layer and an even film thickness help the bag withstand this handling.

Bags splitting around shells, bones and fins

When vacuum is applied, the film is pulled tightly over the product, so sharp edges press directly against it. The PA layer gives the bag its puncture resistance and mechanical strength, which is why PA/PE structures are widely used for frozen seafood. For products with hard shells or bones, the structure and thickness should be chosen with those edges in mind.

Seals that open too easily

The PE layer forms the seal, so its quality matters. But seal strength also depends on the temperature, time and pressure on the packaging machine.

A three-side seal bag is sealed on three edges at the factory, and the fourth is sealed after filling. This means the bag has seal corners, where the side seals meet the bottom seal. These corners take the most stress when the pack is flexed in the freezer or during transport, so they are the first place to check when a bag fails. Wrinkles caught in the final seal, or moisture and fat between the seal surfaces, are other common causes. When a seal fails, check both the film and the machine settings before changing the bag.

Clarity: seeing the product clearly

Buyers and retailers want to see the colour and condition of the seafood through the bag. Clarity depends on the film structure and how it is made. Water-cooled blown film cools quickly, which generally gives better transparency and gloss. Our 7-layer and 9-layer PA/PE vacuum bags are produced on downward water-cooled blown film lines.

What to tell your supplier

To recommend the right bag, we need to know:

• The product: whole fish, fillets or shell-on
• Weight per pack
• Whether the product has sharp edges
• Freezing and storage temperature
• Packaging machine type
• Bag size

If you are sourcing three-side seal vacuum bags for frozen seafood, send us these details and we will suggest a suitable structure. Free samples are available for testing.