How aluminium foil is made: from ingot to retail roll
Between a block of aluminium and the roll in your kitchen drawer there are seven stages, and the quality you end up complaining about is decided in the first three.
Aluminium is cast into slab or strip, hot rolled to a few millimetres, cold rolled to about 0.2 mm, then foil rolled in two stages — often doubled so two sheets pass together — down to 0.006–0.02 mm. It is then annealed to soften it, slit to width, rewound to the length the customer asked for, and packed.
Understanding this sequence explains several things that otherwise look arbitrary: why one side of household foil is shinier than the other, why thin gauge is harder to make than thick, and why the "foil belt" in Henan exists at all — the first three stages need scale, the last three need flexibility, and the two are usually in different buildings.
1. Casting
Aluminium ingots are melted with alloying elements and cast. Two routes dominate:
- DC casting — into large slabs, which are then reheated and hot rolled. Higher quality, more capital, better for critical applications.
- Continuous casting — strip cast directly from the melt at a few millimetres thick. Cheaper and faster, with a narrower range of alloys and slightly less homogeneity.
Melt cleanliness is decided here. Non-metallic inclusions introduced at this stage become the pinholes that appear four stages later — which is why a supplier's pinhole performance at 10 μm is really a statement about their casting and filtration.
2. Hot rolling
The slab is reduced at elevated temperature to a coil a few millimetres thick. This is where the metal's internal structure is set, and where the surface quality of the finished foil begins. A defect rolled in here is still present at 6 μm.
3. Cold rolling
The coil is reduced at ambient temperature down to roughly 0.2 mm, with intermediate annealing to restore ductility. At the end of this stage the material is no longer foil — it is thin sheet — but it is close enough that the foil mills can take it the rest of the way.
Stages 1–3 need scale: a hot mill and a cold mill are large, capital-intensive and run continuously. Stages 4–7 need flexibility: slitting, rewinding and packing are set up per order. This is exactly why foil production concentrates in a few industrial clusters, where coil moves between mills and converters within a short distance rather than crossing the country.
4. Foil rolling
Foil rolling takes the 0.2 mm sheet down to between 6 and 200 μm depending on the product. Two things make it possible:
Roll stacking. At the thinnest gauges two sheets are rolled together as a pack. The top and bottom faces contact the work rolls and come out bright; the two inner faces contact each other and come out matte. This is why one side of household foil is shinier than the other — and why a foil that is bright on both sides at very thin gauge deserves a question.
Tension control. Foil is rolled under substantial tension to keep it flat. Poor tension control produces waves, wrinkles and thickness variation across the width — the defect that makes a roll feed unevenly on a dispenser.
5. Annealing
Rolling work-hardens the metal. Annealing — a controlled heat cycle — restores ductility and produces the "O" temper (soft) that household and catering foil require. The temper is part of the specification: 8011-O and 8011-H18 behave very differently, and the "O" is not optional decoration.
6. Slitting and rewinding
This is where a jumbo coil becomes the product a customer buys. Two operations:
- Slitting — cutting the wide coil into narrower webs. Edge quality is decided here, and blunt blades produce burrs that tear during use.
- Rewinding — winding to the ordered length on the ordered core, at controlled tension. Uneven tension produces the creases that later become tears.
Most quality complaints that reach an importer originate in this stage, not in the mill — because it is the stage with the most handling and the least automation.
7. Printing and packing
Cartons are printed, die-cut and formed; rolls are inserted, sometimes shrink-wrapped, and packed to the carton count on the order. For a private-label product this is where the brand appears, and where most of the schedule risk sits — a print correction can move a shipment by a week.
Frequently asked questions
Why is one side of my foil shiny and the other matte?
Because the foil was double rolled: two sheets passed through the mill together, so the faces touching the work rolls came out polished while the faces touching each other stayed matte. This is normal at thin gauge and is not a defect.
Does the matte side need to face the food?
It makes no measurable difference to performance. The two sides differ in surface topography, not in composition or barrier. Some manufacturers recommend matte-side-in for appearance; the choice is cosmetic.
Why is foil made in such large clusters?
Because the first stages require heavy capital equipment running continuously, while the last stages require flexibility per order. Clustering lets coil move short distances between a mill and several converters, which is why towns like Gongyi in Henan became centres of the industry.
Sources
- The Aluminium Association — Aluminium foil production overview.
- EN 546 series — Aluminium foil technical conditions.
- Related: Pinholes in aluminium foil.