Bagged aluminium foil refers to foil-based flexible packaging formed into pouches, sachets and stand-up bags rather than supplied as plain roll stock. The conversion step, not the foil itself, determines barrier performance: a correctly laminated pouch with a 9 micrometre foil core is effectively impermeable to moisture, oxygen and light, which is why the format has become standard for pharmaceuticals, retort foods, coffee and personal care products.
Where Bagged Foil Sits in the Packaging Range
Plain household foil is used for wrapping and covering, while bagged foil is a laminated structure in which aluminium functions as the barrier layer and the sealant layer provides the bag function. The foil is bonded to a printed outer film for mechanical protection and graphic presentation, and to an inner sealant film that allows heat sealing on vertical form-fill-seal or pre-made pouch lines.
Typical Laminate Structures and Foil Gauges
| Bag type | Typical structure | Foil gauge |
|---|---|---|
| Dry-food sachet | PET / aluminium foil / LDPE | 9 micron |
| Coffee and snack pouch | PET / aluminium foil / PE | 9 - 12 micron |
| Retort pouch | PET / aluminium foil / cast PP | 9 - 12 micron |
| Pharmaceutical strip | PET / aluminium foil / heat-seal lacquer | 20 - 25 micron |
| Heavy-duty chemical bag | PET / aluminium foil / PA / PE | 12 - 25 micron |
Roll stock is specified under ASTM B479 for aluminium foil, and Chinese suppliers commonly reference GB/T 3198 for foil thickness and tolerance classes. Typical packaging lots are ordered as 12 or 20 micron foil in widths that match the laminator, with wetting tension and pinhole density controlled at incoming inspection.
Barrier Performance and Shelf Life
Aluminium foil above roughly 9 micron is treated as a total barrier, provided the layer remains continuous. Water vapour transmission and oxygen transmission of a well-made laminate are therefore governed by edge ingress and by seal quality rather than by the foil film itself. Shelf-life targets are set from the moisture sensitivity of the fill product: crisp and powdered products typically specify a low moisture pickup over twelve to twenty-four months, while pharmaceutical blisters are validated against the pharmacopoeial moisture specification for the dosage form.
Converting, Sealing and Filling Considerations
Seal integrity is the single largest failure mode. Sealant selection must match the filling temperature: cast polypropylene for retort structures sterilised at 121 C, low-density polyethylene for ambient fills, and heat-seal lacquer for blister foil. Machine settings are developed by measuring peel strength and burst pressure across the sealing window, and the window is then frozen in the packaging instruction. Where the bag will be gas flushed or vacuum packed, the pouch geometry and the gusset folds need to be checked for channel leaks at the corners.
Quality and Regulatory Requirements
Structures intended for direct food contact must satisfy the applicable food-contact rules for the metal layer and for each polymer layer, in China GB 4806.9 for metal materials and GB 4806.7 for plastics, with migration testing reported per layer where required. Print adhesion, lamination bond strength, foil continuity and final pouch dimensions are the routine release tests. Traceability from foil coil to finished bag, including lot numbers and lamination adhesive batch, keeps a recall scoped to one production window.
Frequently Asked Questions
Q: Is a 9 micron foil layer really enough to block oxygen?
A: Yes, provided the layer is continuous. Aluminium at that gauge has no measurable permeability, so laminate performance is limited by pinholes, folds and seal quality rather than by the metal.
Q: Why do retort pouches use cast polypropylene as the sealant?
A: Cast PP withstands steam sterilisation at 121 C without softening or delaminating, and it seals cleanly through product contamination in the seal area.
Q: How is pinhole density controlled?
A: By light-table or conductivity inspection of the foil and by inspecting the laminate web, since a single through-thickness defect can dominate the moisture pickup of the whole pouch.
Q: Can bagged foil be used for liquids?
A: Yes, with a suitable sealant and gusset design. Liquids require burst and drop testing on filled bags, and the seal window must be redeveloped for the wet seal area.
Q: What foil thicknesses are stocked for conversion?
A: The common program gauges are 9, 12, 20 and 25 micron, chosen according to barrier requirement, pouch stiffness and the handling forces expected during filling.
Q: Does the outer polyester layer add any barrier?
A: Its main functions are mechanical protection, printability and gloss. It contributes little to moisture or oxygen barrier compared with the foil core.