Specialty Closure Product & Capabilities: Frequently Asked Questions

Specialty closures are engineered sealing solutions designed for specific applications, materials, or performance requirements such as chemical resistance, sterility, or repeated access. Unlike standard caps, they often incorporate liners, septa, or custom geometries to ensure reliable sealing under more demanding conditions.

Closure architecture refers to how a closure is built, not just what materials it contains. It includes how the sealing function is created, where compliance lives, what surface contacts the sample, how the closure handles puncture or repeated access, and how the design performs under compression over time. In other words, architecture is the way the closure distributes different functions across the system.

Selection depends on several factors:

• Container design and interface
• Chemical compatibility
• Required seal integrity and leak performance
• Sterilization method (e.g., gamma, EtO, autoclave)
• User interaction (piercing, resealing, torque requirements)

The biggest risks depend on the application, but common problems include inconsistent sealing force, liner misalignment, long-term compression loss, leakage, analyte loss, contamination ingress, puncture-site damage, coring, particle generation, and loss of resealability. In many cases, the failure is not that the material was obviously wrong. It is that the architecture did not control the real failure mode well enough.

Silicone overmolding allows the compliant sealing element to become part of the cap architecture itself rather than a separate inserted component. This can reduce part count, eliminate loose-liner variation, improve positional control, and localize compliance exactly where the interface needs it. It also allows more intentional sealing geometries. The tradeoff is that overmolding requires tighter design discipline, tooling control, and process control upfront.

No. A more integrated architecture offers more control, but it also reduces some flexibility. In some applications, a separate insert or simpler construction may be the better choice because it supports modularity, easier material changes, or lower complexity. The right architecture depends on the actual interface problem, not on which design appears more advanced.

Historically PTFE has been the top choice for chemical and heat resistance.  Saint-Gobain offers several varieties of PTFE films (skived, cast, porous).  Custom PTFE alternative solutions have also been developed that have been shown to offer better chemical resistance compared to PP and other standard fluoropolymer alternatives on the market.

Because architecture determines how those materials are used. The same silicone, PTFE, or polyolefin may behave very differently depending on whether it is used as a flat insert, part of a laminate, a puncturable septum, a molded sealing feature, or an overmolded region integrated directly into the cap. Performance depends on where the material sits, what function it is assigned, and how the overall interface is designed.

A liner sits between the closure and container to create a seal. It helps prevent leaks, protect contents from contamination, improve chemical compatibility, and maintain product integrity over time.

Selecting the right liner material depends on the application environment and the performance requirements at the sealing interface. Key factors include chemical compatibility with the contents, expected temperature exposure, required barrier properties for moisture or gas, and the material’s ability to maintain compression set and sealing force over time.

A septum is a pierceable elastomeric component that allows needle or spike access while maintaining a seal before and after puncture. It is commonly used in:

• Vials and reagent bottles
• Sampling systems
• Drug delivery applications

An inserted septum makes more sense when the closure also needs to function as an access point, especially for repeated needle puncture. In those applications, puncture mechanics matter much more. Entry force, coring resistance, elastic recovery, and damage accumulation all become central to performance. A standard liner may seal a container, but it is not always designed to survive repeated access gracefully.

The most common mistake is treating the closure as a passive component and assuming that nominal material compatibility is enough. In reality, the closure is often the boundary where contamination, containment, access, compression, and time all meet. When that interface is not designed intentionally, the application can end up relying on assumptions instead of engineering.

Torque matters because it is how many closures are applied, but torque itself is not what creates the seal. The seal depends on the compressive force generated at the interface. Torque is only a proxy for that force, and the translation from torque to sealing load depends on cap stiffness, thread geometry, friction, finish variation, and closure design. That is why two closures applied to the same nominal torque may not create the same sealing performance.

The best starting point is not to ask which material seems best in the abstract. It is to ask what the closure interface must actually do, what failure modes matter most, and where control is needed. If the biggest risk is contamination, that points in one direction. If the biggest risk is repeated puncture, that points in another. If the biggest risk is assembly variation, long-term load decay, or aggressive chemical containment, the architecture choice may change again.

Common methods include:

• Gamma irradiation
• Ethylene oxide (EtO)
• Autoclaving

Material selection must account for potential degradation or property shifts after sterilization.

Seal integrity is typically evaluated using methods such as leak testing, including vacuum decay or dye ingress, along with compression testing, torque or retention testing, and aging studies that help simulate lifecycle performance over time.

The short answer, it depends.  For some custom items, Saint-Gobain has built tools to meet the design and function needs of our customers.  For standard cap options, we typically purchase from an approved manufacturer to take advantage of the lower costs they see from higher production volumes.

No, adhesives add chemicals that we don’t want to introduce to your applications.  Our layers stay together through mechanical bonds made possible from our proprietary extrusion and/or lamination processes.

Yes, we utilize platinum cured silicone which self-heals and prevents leaks once pierced.

Yes, we offer clear, white, or standard colored silicones.  We can customize to meet your performance and cosmetic needs.

Current liner thickness ranges from 20 mils to 145 mils.

We offer caps ranging in size from 8 mm to 89 mm.

We leverage 350 years of material expertise to identify the right material to your application including: polypropylene, polycarbonate, aluminum, phenolic, urea, and PFA.

The most common combination is Silicone & PTFE but we can customize to your application needs with:

• PTFE
• PP
• PFA
• Polyolefin
• Engineered Thermoplastics

We only utilize Platinum Cured Silicone, as peroxide curing process tends to have negative waste/byproducts that we don’t want in our environment.

No, we also support Biopharma, general packaging, diagnostics, etc.  If the application needs a cap and liner, we can do it!

There are several options to ensure the liner stays in the cap.  Press-fit, Microlink® ultrasonic welding, glue fit and can work directly with customers to identify the best solution for the application.