How Aluminium-Plastic Vial Seals Are Manufactured: A Step-by-Step Process

Aluminium-plastic vial seals are made by stamping an aluminium shell from a coated, printed coil, separately moulding a plastic disc or flip button, and assembling the two into a single combination seal that is then inspected and packed under controlled, GMP-aligned conditions. The aluminium provides the crimped, tamper-evident skirt that secures the rubber stopper for container closure integrity; the moulded plastic top provides the flip-off, tear-down, or pull-ring opening feature. Because the finished seal is a primary packaging material in direct contact path with an injectable drug, every stage from incoming coil to final packing runs under a quality system aligned with ISO 15378:2017 and good manufacturing practice.

This guide walks through each manufacturing step, from aluminium coil to packed seal, and explains how contamination control and inspection are built into the process.

Key takeaways

An aluminium-plastic (combi) seal is built from two separately produced parts: a stamped aluminium shell and a moulded plastic top, joined in assembly.
The aluminium starts as a printed, lacquer-coated coil; coating protects the metal and supports later crimping without cracking.
The shell is stamped and formed from the coil; the plastic disc or button is injection moulded and can be matte or glossy, printable, and embossable.
Production for injectable closures runs in classified cleanroom areas (for example, an ISO Class 8 cleanroom) to control particulate and microbial contamination.
High-speed visual inspection screens seals for dimensional and cosmetic defects before packing, supporting the 100% inspection expectations of regulated fill-finish.
The whole sequence is governed by GMP-aligned controls: validated processes, full batch traceability, and contamination control under ISO 15378.

What is an aluminium-plastic seal, and why two materials?

An aluminium-plastic seal is a combination closure: an aluminium shell crimped over the vial stopper, topped with a moulded plastic disc or button that provides the opening feature. The two materials do different jobs. The aluminium skirt is rolled and crimped under the vial flange to hold the elastomeric stopper firmly in place, which is what maintains container closure integrity and gives the seal its tamper evidence. The plastic top adds a clean, removable flip button (or a tear-down or pull-ring feature) so the stopper can be exposed for needle access without disturbing the crimp.

Building the seal from two parts is also what makes it so customisable. The plastic disc can be produced in effectively any colour, matte or glossy, and can be printed or embossed, while the metal can be coloured and printed. This is why a single seal family, such as a flip-off seal, can be supplied in many colour and branding variants without changing the underlying crimp engineering.

Step 1: Aluminium coil, coating, and printing

Manufacturing starts with a coil of pharmaceutical-grade aluminium that is lacquer-coated and printed before any forming takes place. The aluminium is supplied as thin strip on coils. A protective lacquer or coating is applied to the metal so that it resists corrosion and can be deep-drawn and crimped later without the surface cracking or flaking, which matters because loose particles are a contamination risk for an injectable closure.

Printing and colouring happen at the coil stage, while the metal is still flat. Running print and lacquer on flat strip gives consistent registration and a uniform cured film before the metal is stamped into three-dimensional shells. Coating quality is a controlled parameter: film weight and cure are monitored because they affect both the cosmetic finish and the metal’s behaviour during crimping.

Step 2: Stamping and forming the aluminium shell

The coated coil is fed into a high-speed press that blanks and draws each aluminium shell to its finished diameter and skirt height. This is the forming step. Progressive tooling cuts a blank from the strip and draws it into the cup-shaped shell with the central opening and the skirt that will later be crimped onto the vial. Seal sizes are defined here: vial seals are commonly produced in 13 mm, 20 mm, and 32 mm diameters to match standard vial neck finishes.

Dimensional consistency at this stage is critical. The shell’s diameter, skirt length, and the central scoreline or opening must be repeatable across millions of parts, because the seal has to seat and crimp reliably on a high-speed capping station. Tooling wear, strip thickness, and press settings are controlled and the output is sampled to keep dimensions within specification.

Step 3: Moulding the plastic disc or button

The plastic top, the flip button, disc, pull ring, or tear-down feature, is produced separately by injection moulding. Polymer granules are melted and injected into a multi-cavity mould that forms the plastic part along with its tear or flip geometry. The finish is selectable: the plastic disc can be matte or glossy, and it can be printed or embossed for branding, dosage cues, or differentiation.

The moulded part also carries the functional opening feature. For a flip-off seal that means a button with a scoreline that tears cleanly when flipped, leaving the aluminium crimp intact. Different sub-types (bridge, button, and flower or scoreline variants) change how that flip feature behaves; the choice is driven by the regulated market and customer requirements. The polymer and any colourant are selected with the end use in mind, since the plastic forms part of the container closure system and its materials are relevant to extractables and leachables assessment of the finished package.

Step 4: Assembly of metal and plastic

Assembly joins the moulded plastic top to the aluminium shell to create the finished combination seal. The plastic disc or button is fitted into the aluminium shell so the two act as one unit during capping. After assembly the seal is a complete closure ready to be crimped onto a stoppered vial by the drug manufacturer’s capping equipment, where the aluminium skirt rolls under the vial flange to secure the stopper.

It helps to be clear about the boundary here: the seal manufacturer produces and assembles the seal, while crimping the seal onto a filled, stoppered vial happens later, on the pharmaceutical company’s fill-finish line. The seal’s job is to be dimensionally consistent and defect-free so that crimping produces a tight, integral closure every time.

Step 5: Cleanroom handling and contamination control

Seals destined for injectable medicines are handled in classified cleanroom areas so that particulate and microbial contamination is controlled throughout production. Because the seal contacts the stopper and the sterile region of the vial, the environment it is made and packed in matters. Under ISO 15378, manufacturers of primary packaging for sterile products are expected to control cleanliness through defined, monitored environments, gowning, and hygiene practices, and the principle is reinforced by sterile-manufacturing guidance such as EU GMP Annex 1, which frames contamination control as part of overall sterility assurance.

In practice this means cleanroom-classified production and packing zones with controlled air, restricted access, and gowning. A common classification for this kind of work is an ISO Class 8 cleanroom. Handling, transfer, and primary packing of the finished seals take place inside these controlled zones to limit the particles and bioburden that could later compromise the sealed vial.

Step 6: High-speed visual inspection

Finished seals pass through automated high-speed visual inspection that rejects parts with dimensional or cosmetic defects before they are packed. Inspection systems check each seal against defined criteria: diameter and skirt formation, the integrity of the scoreline or tear feature, print quality, and surface defects such as dents, contamination marks, or missing plastic. Defective parts are removed automatically.

This screening supports the wider regulatory expectation that sealed and capped vials receive 100% inspection in fill-finish, an expectation framed by EU GMP Annex 1. A defective seal that reaches the capping line can produce a poorly crimped, leak-prone closure, so screening defects out at the seal-manufacturing stage protects integrity downstream. Inspection results feed the quality records that ISO 15378 requires for traceability and continual improvement.

Step 7: Packing and batch traceability

Inspected seals are packed in protective primary packaging inside the controlled area, with each batch traceable from incoming aluminium and polymer through to the packed units. Packaging protects the seals from contamination and damage in transit and storage. Full batch traceability, a core requirement of ISO 15378, means any issue found later can be traced back through inspection, assembly, moulding, stamping, and the originating raw-material lots so it can be investigated and contained.

How this works in practice at Autofits

Autofits manufactures aluminium-plastic FlipTop® seals and ROPP caps (including Optima, Pull Ring, and Tear Down ranges), tear-off and tear-down aluminium seals, and aluminium pilfer-proof (ROPP) caps at a 75,000 sq ft manufacturing facility in Nashik, Maharashtra that includes an ISO Class 8 cleanroom, producing around 2.4 billion seals per year with a team of 300-plus staff. The lines run high-speed visual inspection, and the plant operates under an ISO 15378:2017 quality system alongside ISO 9001:2015 and ISO 14001:2015 certification and a Drug Master File (DMF). Seals are produced across 13, 20, and 32 mm sizes, with the plastic disc available matte or glossy and printable or embossable and the metal colourable and printable. The combination of a classified cleanroom, automated inspection, and a GMP-aligned quality system is what lets the process described above run at volume while staying inside pharmaceutical contamination-control and traceability expectations. The full certification set is on the quality page.

Frequently asked questions

What are aluminium-plastic vial seals made of?

They are made of two parts: a thin pharmaceutical-grade aluminium shell that is lacquer-coated and crimped over the vial stopper, and a moulded plastic top (the flip button, disc, pull ring, or tear-down feature) that provides the opening mechanism. The aluminium gives tamper evidence and holds the stopper for closure integrity, while the plastic gives the easy-opening feature and the printable, colourable finish.

How are flip-off seals manufactured?

The aluminium shell is stamped and drawn from a printed, coated coil; the plastic flip button is injection moulded separately with its scoreline; the two are assembled into one seal; and the finished seals are inspected and packed under cleanroom conditions. The seal is later crimped onto a stoppered vial on the drug manufacturer’s capping line, where the plastic button flips off to expose the stopper while the aluminium crimp stays in place. See how flip-off caps work for the opening mechanism in detail.

Why are vial seals made in a cleanroom?

Because the seal is a primary packaging material that contacts the stopper and the sterile region of an injectable vial, so particulate and microbial contamination must be controlled during its manufacture. Producing and packing seals in classified cleanroom areas, such as an ISO Class 8 cleanroom, limits the contamination that could later compromise a sealed vial. This contamination-control expectation is built into ISO 15378 and reinforced by sterile-manufacturing guidance like EU GMP Annex 1.

What is the difference between the aluminium part and the plastic part?

The aluminium part is the structural, crimped shell that secures the rubber stopper and provides tamper evidence and closure integrity. The plastic part is the moulded top that provides the opening feature (flip, tear-down, or pull-ring) and carries colour, print, and embossing. Making them separately and assembling them is what allows wide customisation without changing the crimp engineering. See what an aluminium-plastic seal is for more.

How are vial seals inspected for defects?

Finished seals pass through automated high-speed visual inspection that checks each part against defined criteria (diameter, skirt formation, scoreline integrity, print quality, and surface defects) and automatically rejects nonconforming seals before packing. This screening supports the 100% inspection expectation for capped vials in fill-finish and feeds the traceability records required by ISO 15378.

Does the seal manufacturer crimp the seal onto the vial?

No. The seal manufacturer produces, assembles, inspects, and packs the seal. Crimping the seal onto a filled, stoppered vial happens later on the pharmaceutical company’s fill-finish line, where the aluminium skirt is rolled under the vial flange to secure the stopper. The seal’s role is to be dimensionally consistent and defect-free so that crimping produces an integral closure.

Sources

ISO: ISO 15378:2017, Primary packaging materials for medicinal products (https://www.iso.org/standard/70845.html)
European Commission, EudraLex Volume 4, GMP Annex 1, Manufacture of Sterile Medicinal Products (https://health.ec.europa.eu/medicinal-products/eudralex/eudralex-volume-4_en)
ICH: Q9 Quality Risk Management (https://www.ich.org/page/quality-guidelines)

*Last updated: 2026-06-10. This article is general technical and regulatory information, not legal or compliance advice; confirm current standard editions with ISO and the relevant regulator.*