Lyophilization Vial Seals

A lyophilization vial seal is the aluminium-plastic flip-off seal crimped over the stopper of a freeze-dried vial once the drying cycle is finished and the stopper has been seated inside the chamber. Autofits supplies them in 13 mm and 20 mm: total seal height 7.62 to 8.38 mm and 9.02 to 9.91 mm, with maximum opening forces of 30 N and 35 N. Larger freeze-dry vials in 28, 32 and 34 mm are served by the same FlipTop® Optima range.

What makes a lyo seal different from an ordinary vial seal happens on the line, not in the part. This page covers the partial-stoppering sequence, crimp consistency, the integrity position, dimensions and supply.

Key takeaways

The seal is crimped after lyophilisation, outside the freeze-dryer, over a stopper seated inside the chamber.
During the cycle the two-leg stopper sits half-inserted so water vapour can leave the vial; the chamber is then backfilled and the shelves press the stoppers fully home.
Autofits supplies lyo seals in 13 mm and 20 mm, with 28, 32 and 34 mm in the same Optima range.
Maximum opening force is 30 N at 13 mm and 35 N at 20 mm, with six tapered bridges at both sizes.
The crimp is the last barrier on a hygroscopic cake, so dimensional consistency across the batch matters most.
Integrity is evaluated against USP <1207>; aseptic capping falls under EU GMP Annex 1.

What a lyophilization vial seal is

A lyophilization vial seal is a standard aluminium-plastic flip-off seal used in a non-standard sequence: applied after freeze-drying rather than at fill, over a freeze-drying stopper whose seated profile differs from an ordinary injection stopper. The seal itself is a combi seal, an AA8011 aluminium shell with a moulded polypropylene button, made to ISO 8362-6.

What is specific to lyophilisation is the stopper, not the cap. Freeze-drying stoppers are covered by ISO 8362-5 and carry legs or slots so the stopper can rest proud of the neck during drying. The seal that goes over one is the same family used on a serum vial; what changes is when it is applied and how much rides on the crimp. The flip-off design fits the workflow because it leaves the aluminium permanently crimped and opens only a small central injection point, the right access pattern for a powder reconstituted by injecting diluent through the stopper.

Partial stoppering and where the seal comes in

The freeze-dry cycle runs with the stopper half-inserted, and the vial is crimped only after it has left the lyophiliser. The sequence is fixed:

Vials are filled and the two-leg stopper is placed in the half-seated position, leaving a vapour path out of the vial.
The shelves are frozen, then the ice is sublimed under vacuum through primary and secondary drying.
The chamber is backfilled, commonly with nitrogen, and the shelves press down so every stopper is fully seated. The chosen headspace is locked in at this point.
The vials are unloaded and the seal is crimped over the seated stopper outside the lyophiliser.

Two things follow. The stopper has already made the closure before the seal arrives, so the seal preserves it rather than creates it. And the vial is not stable between unload and crimp, because the stopper is held only by friction. EU GMP Annex 1 addresses that window: vials with missing or displaced stoppers must be rejected before capping, and stoppered vials are kept under grade A air supply until the cap is crimped. Its lyophilisation provision came into operation on 25 August 2024.

Post-lyo crimp force and why consistency matters

On a freeze-dried product the crimp is the only mechanism holding residual compression on a stopper seated under vacuum or backfill, so a seal that crimps inconsistently across a batch puts the headspace and the cake at risk. On a liquid fill an under-crimped vial is a defect; on a lyophilised fill it is also a stability problem, because the cake is often hygroscopic and the headspace composition is part of the specification.

Three seal properties govern how repeatable the crimp is, and all three are dimensional:

Inner aluminium diameter and skirt height, which must match the neck finish and the seated height of the freeze-drying stopper so the skirt rolls evenly under the flange.
Aluminium thickness, held to 0.16 to 0.20 mm at both sizes. Drift changes the force the capper needs and the springback the closed seal has.
Bridge geometry. Both sizes use six tapered bridges, which is what sets opening force at 30 N and 35 N.

Particle control matters more here too, because the vial is open at the neck for the whole drying cycle and again at unload. Ready-to-Use seals are washed, assembled in an ISO Class 8 cleanroom and double-bagged.

Container closure integrity after lyophilisation

Integrity is evaluated on the finished, crimped container against the package-integrity methods in USP General Chapter <1207>, which separates deterministic leak tests such as vacuum decay and helium leak detection from probabilistic methods. Deterministic methods carry extra weight here: headspace analysis confirms the backfill gas is still present at the specified level, a direct read on whether the closure has held since capping. Method selection is covered under container closure integrity testing, and the residual-moisture and stability context on the lyophilised products page.

Specifications and sizing

FlipTop® Optima dimensions at the two lyophilisation sizes, from the Autofits engineering drawings. Shipper box 420 × 270 × 320 mm.

Property	13 mm	20 mm
Inner Ø aluminium seal (D1)	13.36 mm (min)	20.22 mm (min)
Outer Ø disc (D2)	14.99 mm (max)	23.14 mm (max)
Disc height	2.90–3.30 mm	3.20–3.60 mm
Inner aluminium height	6.15–6.40 mm	7.37–7.62 mm
Total seal height	7.62–8.38 mm	9.02–9.91 mm
Aluminium thickness	0.16–0.20 mm	0.16–0.20 mm
Bridges	6 taper	6 taper
Max opening force	30 N	35 N
Standard packing per box	15,000 (5,000 × 3 bags)	6,000 (2,000 × 2 bags)

Larger freeze-dry vials use the same Optima range: 28 mm at 27.60 to 28.20 mm inner diameter, 11.06 to 12.06 mm total height, eight bridges, 35 N; and 32 mm at 32.10 to 32.90 mm, 14.30 to 15.50 mm, twelve tapered bridges, 65 N. Per-size detail is on the 13 mm, 20 mm and 28 mm pages. The Button design adds intrinsic tamper evidence, a 12-stem flower moulded under the button disc.

Materials and quality

The shell is AA8011 aluminium alloy to EN 15088:2005, supplied with EN 10204 3.1 certification and tested to BS EN 485-2:2008, REACH and RoHS compliant, with an epoxy lacquer coating to 21 CFR 175.300. The button is polypropylene to IS 10910, IS 10909, FDA 21 CFR 177.1520 and EC 1895/2005, with BADGE, NOGE and BFDGE not used, moulded in-house on Japanese Toyo injection machines. Heavy metals are limited to a maximum 100 ppm total to EN 602 and EC 94/62, and components are BSE/TSE-free to EMEA/410/01 rev. 3.

Washing is fully automated, assembly is in an ISO Class 8 cleanroom in the 75,000 sq ft Nashik facility, and every seal passes 100% high-speed camera inspection. AQL is critical nil, major NMT 2.5%, minor NMT 4%, tailorable. Production runs under ISO 15378:2017, ISO 9001:2015 and ISO 14001:2015, with a Drug Master File (DMF 18100) and CFDA registration; certificate numbers are on the quality page.

Forms of supply and applications

Lyophilization vial seals ship Regular (non-sterile), Ready-to-Use or Ready-to-Sterilize. Ready-to-Use is the usual specification for an aseptic freeze-dry line: washed and assembled in the ISO Class 8 cleanroom, double-lacquered, sterilized by gamma irradiation or ethylene oxide and double-bagged for aseptic areas. Shelf life is 3.5 years before capping for non-irradiated seals, plus 5 years after capping, and 2 years for Ready-to-Use. Minimum order quantities, pricing and lead times are available on request.

Freeze-drying is used for molecules that are not stable in solution, so lyo seals go onto biologics, lyophilised antibiotics, oncology agents and cell and gene therapy intermediates. Many ship as a two-part kit with a separate diluent, so a site often runs a liquid line alongside the freeze-dry line and specifies the same seal family for both.

Frequently asked questions

What is a lyophilization vial seal?

It is the aluminium-plastic flip-off seal crimped over the stopper of a freeze-dried vial after the lyophilisation cycle has finished. The stopper is seated inside the freeze-dryer at the end of the cycle, the vials are unloaded, and the seal is crimped outside the chamber. It holds the stopper compressed against the glass so the closure made under controlled conditions is preserved for the shelf life.

Why is the stopper only half-inserted during freeze-drying?

A freeze-drying stopper has legs or slots so it can rest in a raised, half-seated position on the vial neck. That gap is the vapour path: it lets water leave the vial during sublimation. If the stopper were fully seated at the start, the ice could not sublime out. At the end of the cycle the chamber is backfilled and the shelves press every stopper fully home.

When is the vial crimped in a lyophilisation process?

After the vial leaves the lyophiliser. The order is fill, half-seat the stopper, freeze and dry, backfill the chamber and seat the stoppers with the shelves, unload, then crimp. Between unload and crimp the stopper is held only by friction, which is why vials with missing or displaced stoppers are rejected before capping.

What sizes are lyophilization vial seals made in?

Autofits supplies them in 13 mm and 20 mm. The 13 mm seal has an inner aluminium diameter of 13.36 mm minimum, a total height of 7.62 to 8.38 mm and a maximum opening force of 30 N; the 20 mm seal is 20.22 mm minimum, 9.02 to 9.91 mm and 35 N. Larger freeze-dry vials are served in 28, 32 and 34 mm from the same range.

Why does crimp consistency matter more on a lyophilised product?

Because the cake is often hygroscopic and the headspace gas composition is part of the specification. The crimp is the only mechanism holding residual compression on a stopper seated under vacuum or backfill, so a seal that crimps unevenly can let residual seal force fall below what keeps the vial gas-tight. Ingress then raises residual moisture, collapses the cake or degrades the molecule.

Sources

ISO: ISO 8362-5, Injection containers and accessories, Part 5: Freeze drying closures for injection vials (https://www.iso.org/)
ISO: ISO 8362-6, Injection containers and accessories, Part 6: Caps made of aluminium-plastics combinations for injection vials (https://www.iso.org/)
USP: General Chapter <1207>, Package Integrity Evaluation, Sterile Products, in the USP-NF (https://www.usp.org/)
EudraLex Volume 4, EU GMP Annex 1, Manufacture of Sterile Medicinal Products (https://health.ec.europa.eu/medicinal-products/eudralex/eudralex-volume-4_en)
Autofits engineering drawings and FlipTop Seals dossier (internal, on file)

*Last updated: 2026-08-18. This page is general technical and product information, not regulatory or compliance advice; confirm current standard editions, material specifications and your own specification with the Autofits technical team and the issuing bodies.*