Single-serve coffee capsules use two different aluminium foils: a thicker, deep-drawable foil for the cup body and a thin, heat-seal-lacquered foil for the lid that the machine pierces. This guide explains which alloys, tempers, gauges and coatings suit each part, and what capsule makers should specify when they buy foil stock.
Ground coffee starts to stale within hours of grinding, because oxygen attacks the aromatic oils and moisture accelerates the process. A capsule has to hold a few grams of coffee for months, then survive brewing pressures of around 15–19 bar and temperatures above 90 °C. Aluminium foil does both jobs with a very thin wall.
Rolled aluminium foil above roughly 20 µm is effectively free of pinholes, so it forms an almost total barrier to oxygen, water vapour and light. That is why aluminium capsules can be flushed with nitrogen, sealed and stored without a secondary oxygen-barrier pack, whereas many plastic or compostable capsules need an outer bag. Aluminium also conducts heat well, deep-draws into thin-walled cups at high speed, and is fully recyclable without loss of quality.
The capsule maker does not buy finished foil off the shelf. Body and lid stock are usually ordered as lacquered or printed coils slit to the width of the press or lidding line, with the alloy, temper, gauge and coating system agreed in advance and confirmed by trials.
Three alloy families cover almost every aluminium capsule on the market. The composition limits below are the registered Aluminum Association values; the mill certificate for each coil reports the actual analysis.
| Alloy | Main alloying elements | Typical use in capsules | Why it is chosen |
|---|---|---|---|
| 8011 | Fe 0.6 – 1.0 %, Si 0.5 – 0.9 % | Body foil and lid foil | Iron-silicon particles give a fine grain and good strength-to-ductility balance for deep drawing; widely available |
| 3003 | Mn 1.0 – 1.5 %, Cu 0.05 – 0.20 % | Body foil for deeper or stiffer cups | Higher strength and dent resistance; holds shape on deep, complex forms |
| 1235 | Al ≥ 99.35 % | Lid foil, laminated lid structures | Very soft and ductile, low pinhole count at thin gauges, pierces cleanly |
| 8079 | Fe 0.7 – 1.3 %, Si 0.05 – 0.30 % | Lid foil | Higher iron raises strength and puncture resistance of thin O-temper foil while keeping ductility |
All capsule foils are normally supplied in the fully annealed O temper. Annealing removes the rolling oil and gives the high elongation needed for drawing or for a lid that must stretch slightly under brew pressure before it ruptures against the pyramid plate of the machine. Some lid designs use a light H-temper to stiffen the foil; this is agreed with the capsule designer.
The cup is formed in several stages on a multi-cavity press from lacquered coil. Defects in the foil appear immediately as split walls, wrinkled flanges or uneven height. Buyers should control the following:
| Property | Typical target | Why it matters |
|---|---|---|
| Gauge | About 0.08 – 0.12 mm (a common cup wall is near 0.10 – 0.11 mm) | Thinner saves metal; too thin risks splitting and denting |
| Gauge tolerance | Commonly ± 4 – 5 % or tighter by agreement | Uniform wall height and consistent press set-up |
| Temper | O (annealed) | Maximum elongation for deep drawing |
| Earing | Low, agreed by cup test | Earing creates uneven flanges that fail the seal |
| Inner coating | Food-contact lacquer, typically 3 – 6 g/m² | Separates coffee from metal, resists hot water and oils |
| Outer coating | Colour lacquer or print primer, sometimes embossed | Brand colour, scuff resistance, machine recognition |
| Surface | Clean, dry, free of oil, pinholes and scratches | Lacquer adhesion and visual quality |
Earing is the waviness at the rim of a drawn cup caused by crystallographic texture in the foil. Mills control it through the rolling and annealing schedule; for capsule work it is worth asking for cup-test results on the first coils of a new supply.
Lid foil is usually around 30 – 40 µm thick before embossing. It is coated on the inside with a heat-seal lacquer chosen to bond to the body material: aluminium cups use a lacquer compatible with the body inner coating, while plastic cups need a lacquer that bonds to polypropylene, polystyrene or PET. The outside is printed or colour-lacquered.
The lacquer must give a peel strength high enough to hold through filling, nitrogen flushing and transport, yet the seal must not leak under brew pressure. Seal temperature, dwell time and pressure are set on the lidding machine in trials.
At 30 µm and above, rolled foil is essentially pinhole-free. The lid therefore keeps oxygen and moisture out as effectively as the body.
Some systems pierce the lid with needles; others let it rupture against a patterned plate as pressure builds. Foil gauge, temper and embossing pattern control how cleanly and repeatably this happens.
Some lids combine foil with a thin polymer layer for extra seal strength on plastic cups or to control tearing behaviour.
A fine embossed pattern stiffens the lid, reduces wrinkles during sealing and helps the foil feed on high-speed lines.
Lids are either pre-cut and stacked, or cut and sealed in one step from a narrow coil. The coil format must suit the lidding line.
The lacquer system is as important as the metal. Inner coatings on body and lid are in direct contact with hot coffee, so they must comply with the food-contact rules of the market where the capsules are sold. In the European Union that means Regulation (EC) No 1935/2004 and good manufacturing practice under Regulation (EC) No 2023/2006; in the United States, coatings are typically formulated to FDA 21 CFR 175.300. The aluminium itself should meet the composition limits of EN 602 for food-contact semi-products.
A common mistake is to approve foil on a datasheet alone. Small differences in temper, lacquer cure or surface cleanliness can change forming and sealing behaviour, so a short trial run on the real tooling is essential.
Reference standards for foil dimensions and tolerances include EN 546 and ASTM B479.
Capsule bodies are usually drawn from about 0.08 – 0.12 mm foil, with many standard cups close to 0.10 – 0.11 mm. Lids are normally about 30 – 40 µm before embossing.
8011-O is the most common choice because it deep-draws well and is widely available. 3003-O is used when the cup is deeper or needs more stiffness and dent resistance.
The alloy can be the same (8011 is used for both), but gauge and coatings differ: the body needs a thicker foil with a forming-grade lacquer, while the lid needs thin foil with a heat-seal lacquer matched to the body.
Yes, if the heat-seal lacquer is formulated for that polymer, such as polypropylene. The lacquer must be specified for the body material and confirmed in sealing trials.
The aluminium is fully recyclable. In practice recovery depends on local collection schemes and on separating the used coffee grounds from the capsule.
Alloy and temper, gauge and tolerance, coating system for each side, slit width, coil diameter and core, quantity and destination. Metline can supply samples for forming and sealing trials.
Send your body and lid specifications. We will reply with suitable alloys, coating options, samples and a delivered price.
