ISO 8362-5: Freeze-Drying Closures for Injection Vials

ISO 8362-5 is the international standard that specifies the freeze-drying (lyophilisation) closures for injection vials: the slotted rubber stoppers designed to let water vapour escape during drying before the vial is sealed. These closures sit part-way in the vial during the freeze-drying cycle, with slots or legs that keep a vapour path open, then are pushed fully home to seal the vial at the end of the cycle. It is Part 5 of the ISO 8362 series, “Injection containers and accessories.” The current edition is ISO 8362-5:2016.

This guide explains what ISO 8362-5 covers, how a freeze-drying closure works, and how it differs from a standard vial closure.

Key takeaways

ISO 8362-5 specifies the freeze-drying closures for injection vials: the slotted stoppers used in lyophilisation.
It is Part 5 of the ISO 8362 series; the current edition is ISO 8362-5:2016.
A freeze-drying closure is a specialised elastomeric closure with slots or legs that let water vapour escape during the drying cycle.
During freeze-drying the stopper sits in a raised position; at the end of the cycle it is pushed fully home to seal the vial under vacuum or inert gas.
Standard (non-slotted) closures are covered by ISO 8362-2; the freeze-drying version has its own part because of its distinct geometry.
The stopper is then secured by an aluminium or aluminium-plastic seal crimped over it, the same as any vial closure.

What is ISO 8362-5?

ISO 8362-5 is the part of the ISO 8362 series that defines the rubber closures used for freeze-drying (lyophilisation) of products in injection vials. It is published by the International Organization for Standardization (ISO), and the current edition is ISO 8362-5:2016.

Freeze-drying, or lyophilisation, removes water from a product by freezing it and then drawing off the ice as vapour under vacuum. The challenge for the closure is that the vial has to stay open enough during the cycle for vapour to leave, but be sealable inside the freeze-dryer once drying is complete, without opening the chamber. The freeze-drying closure solves this with a special shape: it is a rubber stopper with slots or legs so that, when it sits in a raised (part-inserted) position in the vial mouth, vapour can still pass out around it. ISO 8362-5 standardises the forms, dimensions, and requirements of these closures.

How a freeze-drying closure works

A freeze-drying closure works by holding a vapour path open during drying, then sealing the vial when it is pressed fully home at the end of the cycle inside the freeze-dryer. The sequence is:

The filled vials are loaded into the freeze-dryer and the slotted stoppers are placed in a raised, part-inserted position in the vial mouths.
During the freezing and drying stages, the slots or legs of the stopper keep a path open so water vapour can escape from the vial.
When drying is complete, the freeze-dryer’s shelves press down on the stoppers, pushing them fully into the vial mouths to seal the vials, often under vacuum or an inert gas, without breaking the chamber’s controlled environment.
The sealed vials are removed and an aluminium or aluminium-plastic seal is crimped over each stopper to hold it in place, the same finishing step as any vial.

This is why the freeze-drying closure needs its own part in the series: a standard closure would either block the vapour path or not seat correctly for the two-position cycle. The slotted design is purpose-made for lyophilisation.

Freeze-drying closure vs standard closure

A freeze-drying closure differs from a standard vial closure in its shape: it has slots or legs to allow vapour out during drying, and it is used in two positions (raised, then fully seated). A standard closure, covered by ISO 8362-2, is simply seated once when the vial is filled.

Aspect	Standard closure (ISO 8362-2)	Freeze-drying closure (ISO 8362-5)
Shape	Solid plug and flange	Plug with slots or legs for vapour escape
Use	Seated once at filling	Raised during drying, then pushed fully home
Application	Liquid and other injectables	Lyophilised (freeze-dried) products
Finishing	Aluminium or aluminium-plastic seal crimped over	Aluminium or aluminium-plastic seal crimped over

After the freeze-drying cycle, both closure types are finished the same way: an aluminium or aluminium-plastic seal is crimped over the stopper and vial neck to hold it compressed and maintain the seal, the step explained in how flip-off caps work.

How this works in practice at Autofits

The freeze-drying closure is the specialised rubber stopper; Autofits manufactures the aluminium and aluminium-plastic seals that crimp over it to finish the vial, regardless of whether the product was lyophilised. The range includes FlipTop Optima flip-off seals, tear-off and tear-down aluminium seals, and aluminium pilfer-proof (ROPP) caps, in 13, 20, and 32 mm sizes (the full products page lists the range). Freeze-dried injectables, including many vaccines and biologics, are sealed with the same crimped aluminium or aluminium-plastic seals once the slotted stopper has been pushed home. Autofits produces these seals under an ISO 15378:2017 quality system, alongside ISO 9001:2015 and ISO 14001:2015 certification and a Drug Master File, in a 75,000 sq ft Nashik facility with an ISO Class 8 cleanroom and high-speed visual inspection. The full certification set is on the quality page.

Frequently asked questions

What does ISO 8362-5 cover?

ISO 8362-5 specifies the freeze-drying (lyophilisation) closures for injection vials: the slotted rubber stoppers that let water vapour escape during drying. It is Part 5 of the ISO 8362 series and standardises the forms, dimensions, and requirements of these closures, which have a distinct geometry from the standard closures of ISO 8362-2.

How is a freeze-drying stopper different from a normal stopper?

A freeze-drying stopper has slots or legs so that, when it sits in a raised, part-inserted position, vapour can escape from the vial during drying. A normal stopper is a solid plug seated once when the vial is filled. The freeze-drying stopper is used in two positions: raised during the cycle, then pushed fully home to seal the vial at the end.

When is the vial sealed during freeze-drying?

The vial is sealed at the end of the drying cycle, inside the freeze-dryer, when the shelves press down on the slotted stoppers and push them fully into the vial mouths, often under vacuum or inert gas. This seals the product without exposing it to room air. An aluminium or aluminium-plastic seal is then crimped over the stopper to hold it in place.

What is the current edition of ISO 8362-5?

The current edition is ISO 8362-5:2016. ISO standards are reviewed periodically, so confirm the current edition and its requirements directly with ISO before relying on any specific clause.

Are freeze-dried vials sealed with the same aluminium seals as other vials?

Yes. Once the slotted freeze-drying stopper is pushed fully home, the vial is finished the same way as any injectable vial: an aluminium or aluminium-plastic seal is crimped over the stopper and the vial neck to hold the stopper compressed and maintain the seal. The freeze-drying closure is specialised; the finishing seal is standard.

Sources

ISO: ISO 8362-5:2016, Injection containers and accessories, Part 5: Freeze drying closures for injection vials (https://www.iso.org/standard/65448.html)
ISO: ISO 8362-2:2024, Injection containers and accessories, Part 2: Closures for injection vials (https://www.iso.org/standard/87251.html)

*Last updated: 2026-06-18. This article is general technical information, not regulatory or compliance advice; confirm current standard editions and requirements with ISO.*