From rubber stoppers to screw thread closures, snap caps to aluminum seals, DWK Life Sciences completes your package with the right closure for your application. Our comprehensive range of caps and closures ensures that you get the perfect fit for your container and chemical compatibility with your samples. Our caps conform to GPI (Glass Packaging Institute) standards and ISO and ASTM specifications, as well as European DIN specs.

To best support, your efforts, all of our plastic and aluminum caps and closures are manufactured from the highest quality raw materials and to yield exceptional dimensional stability.

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Perfectly Matched Caps and Closures

We understand that in your work there are multiple reasons for needing a stopper or seal. That’s why we offer a full line of sizes and styles, including rubber formulations to support lyophilization, multiple piercings, resist gas and moisture transmission, autoclave, high heat, and chemical resistance. You can trust that all of our stoppers are manufactured from the highest quality raw materials with exceptional dimensional stability. The most common stopper styles for standard storage applications include:

  • Straight-plug stoppers which provide maximum sealing for vials with straight-wall glass finish
  • Snap-on style stoppers which deliver maximum sealing for vials with a blow-back glass finish
  • Sleeve style stoppers which feature a fold-over skirt for sealing serum finish vials without a crimp closure.

Our lyophilization stoppers come in igloo, two-leg and three-leg styles giving one, two, or three venting points. If you’re looking for a stopper with extremely high chemical purity and low gas permeability, we recommend our Ultra Pure stoppers, manufactured from a bromobutyl formulation and compliant with US, European, and Japanese Pharmacopeias. A wide selection of borosilicate glass stoppers is available that includes medium, full length, and standard taper that are perfectly matched with glass flasks, cylinders, and funnels.

If your search for caps and closures leads you to look for septas and liners, DWK Life Sciences offers a variety of sizes and materials to meet your needs. Used in combination with screw caps or aluminum seals, these lab essentials provide leak proof seals, protect the cap from aggressive agents and chemicals, and enable easy access to the contents with a syringe. Also available as a red PFTE faced silicone rubber septa that provides exceptional compressibility and resealability. PTFE-faced silicone rubber septa are autoclavable, resist coring, and are recommended for use in all autosamplers using screw thread vials.

Septa and liners can be laminated with PTFE on one or both sides to provide high chemical resistance and a nearly inert barrier between sample and septa material.

If you’re working with sample and media storage containers made of glass and plastic, the most common closure liner materials/styles for screw caps that we recommend includes poly-vinyl, foamed polyethylene (PE), metal foil/pulp, and polyethylene cone. Poly-vinyl liners can be used with mild acids, alkalis, solvents, and alcohols. Foamed polyethylene (PE) liners provide excellent chemical resistance for acids, alkalis, solvents, alcohols, oils, and aqueous products. We suggest our foil/pulp liners if your work demands good barrier properties and resistance to hydrocarbons, oils, ketones, and alcohols. Polyethylene cone liners are a unique problem-solving liner. Their innovative cone design provides a wedge type seal that not only seals across the top but also across the inside diameter of the container. In addition, we’ve made sure that they’re crack resistant, offer superior torque retention, and have excellent sealing properties.

Our seals are ideally suited for long-term sample storage and lyophilization applications. Our aluminum seals, designed for use with GPI serum finish vials and bottles, are available in a wide range of colors, styles, and sizes. The convenient open top septa provides direct access to simplify content removal. Another alternative, solid top seals, provide maximum protection from evaporation. Flip off, tear off, and tear out styles provide reassuring tamper evidence. Center disc tear-out seals are commonly used with serum or molded vials requiring stopper exposure for syringe access. Our aluminum tear-off versions can be completely removed from the vial or bottle to facilitate access to vial contents. Be advised, you’ll need to use a crimping or decapping tool to apply or remove aluminum seals from containers with crimp top and should consider one of our manual or automated crimping tools.

Consider threaded screw closures for containers used for mixing, extended storage, transport, and delivery of liquid media, buffer solutions, culture media, non-hazardous chemicals or volatile organic substances and solvents. We offer many choices in screw closures including PTFE, PBT, PE, and black phenolic styles. A variety of liner options ensure compatibility with a wide range of chemicals. In line with our commitment to quality, all of our caps are made from high-quality materials and conform to GPI (Glass Packaging Institute) standards and ISO and ASTM specifications, as well as European DIN specs.

DWK Life Sciences I-Loc closures combine the advantages of an aluminum seal with the convenience of a screw cap. The innovative design consists of an open-top polypropylene (PP) screw cap, which is connected to a gray bromobutyl stopper. I-Loc closures are available in five different colors and can be autoclaved.

Closures for media bottles are available in linerless polypropylene screw thread caps that are an economical autoclavable solution with exceptional sealing qualities. They are available with an internal molded seal ring and in solid and open-top formats. Open top caps can be used in combination with bromobutyl rubber GL 45 stoppers to assist you with applications requiring a gas-tight seal of the container, such as storage of oxygen-sensitive materials or maintenance of anaerobic culture conditions.

Our premium caps, made from pigment-free polymer, reduce the risk of leaching and PTFE-faced silicone cap liners maximize leak tightness. We also offer tamper-evident PP screw caps for media and sample storage bottles to help preserve your samples and your piece of mind. The robust and durable three-hole cap systems provide tubing connection/distribution caps for the easy transfer of liquids or gases in and out of bottles under controlled conditions, reducing the risk of contamination or spillage. Multiple port connection screw caps are available to fit the various glass thread finishes on commonly used laboratory bottles such European DIN GL 25/32/45 and GLS 80 thread standards. Some of the distribution caps accept the semi-rigid PEEK, PFA, FEP or PTFE tubing, while others can be used with flexible silicone tubing and hoses. We’re happy to help you select the perfect cap if you have any doubts. Connector elements are also available for probes and stirrers.

We offer snap caps that come in a variety of styles and colors as well as a variety of materials for both the cap and the liner. The real innovation here is how quick and easy it is to snap on and snap off the caps. These caps are an especially convenient choice for applications that do not require heating of the sample above room temperature and where some evaporation can be tolerated. For example, they’re a perfect cap for sample collection and storage or simple chromatographic analysis using snap ring vials.

KIM-KAP® slip-on caps are a series of disposable polypropylene slip-on style closures used on culture tubes and culture flasks. For your convenience, they come in five colors — natural, red, green, yellow, and blue — to allow color coding and they’re autoclavable. These caps can also be used as a dust cover for burets.

Frequently Asked Questions

Choosing the right septa and closures for your analysis is critical to ensure chemical compatibility with your sample and solvents and protect sample integrity and prevent contamination. Screw and snap caps are usually made of plastic, mostly polypropylene (PP) or polyethylene (PE), whereas seals for crimp-top vials are made from aluminum. For applications involving automated transport of vials, magnetic caps are recommended. The cap liner or septa is the part of the cap which establishes a tight seal with the vial. Liners and septa can be laminated with PTFE on one or both sides, which results in high chemical resistance and a nearly inert barrier between sample and septa material.

Our closures and liners are designed for a variety of applications. Our chemical compatibility chart will help you to find containers and cap materials that fulfill the requirements of your application/experiment. However, please keep in mind that product performance can vary depending on conditions. It is recommended that proper tests be performed to determine the best product combination for the application. If you still have questions, we’re here to help.

The American Glass Packaging Institute (GPI), American Society German Institute for
Standardization of the Plastics Industry (SPI), and German Institute for Standardization (DIN - GL thread) are responsible for establishing the international standards for glass and plastic container neck finishes that are commonly used in laboratories. Despite the standardized dimensions, we need to caution you that there may still be compatibility issues between containers and caps coming from different manufacturers; therefore, it is advantageous to buy both container and screw closure from the same source whenever possible. Similar to the packaging industry, when a closure finish is designated as 33-400, it means that the nominal diameter measured across the inside of the closure at the opening is approximately 33 mm. The 400 designates a specific style of thread. Keep in mind, the thread finish of the closure and container must be the same. A container with a 33-400 thread finish should be used with a closure that has a 33-400 thread finish. A similar nomenclature guideline applies to the GL thread system in which the number (25, 32 or 45) corresponds to the outer diameter of the thread in mm, for example, a GL 45 thread has an outer diameter of 45 mm. For containers with crimp finish, seals and stoppers are selected based on the mouth OD of the vial. For example, a 20 mm crimp top vial (mouth OD = 20 mm) has to be combined with a 20 mm stopper and a 20 mm seal. A corresponding 20 mm crimping and decapping tool is needed to apply and remove the seal from the vial.

Your choice should be based on the application’s chemical and temperature exposure
requirements. For example, the blue polypropylene caps are liner-less, made of chemical
resistant material, and well suited to many general laboratory applications. If a higher chemical or temperature resistance (to 180 °C) is required we recommend the red PBT (polybutylene terephthalate) cap. Our PBT caps have PTFE-faced liners, meaning that they are an excellent option for long-term sample storage or shipping (ASTM D4991-07 (2015)). GL 25 and GL 45 bottle caps made of PFA are available as liner-less or with cap liners are suitable for the most demanding applications in the pharmaceutical industry including dry heat sterilization (to 200°C).

Crimp closures are generally well known for their excellent sealing characteristics — an absolute must to maintain parenteral content integrity and long-term sample storage. It has to be noted, however, that the quality of a crimp seal is strongly dependent on the right calibration of the crimping tool used to apply the closure to the vial. To maintain good results, make sure to re-calibrate your crimping tool regularly and check the quality of the seal every time you crimp. The best way to know if your vial has been crimped properly is to visually inspect the overall appearance of the crimp.

An optimal crimp result is characterized by the following features:

  • The cap surface is flat.
  • The sides of the cap fit tightly around the vial neck and do not show any deformations.
  • The septa is not being sucked into the vial nor does it emerge out of the center hole.

Many of our customers rely on the so-called “turning test” or “twist test” to verify the crimp result. To test the quality of the crimp, the vial is held in one hand while the other hand is used to test whether the crimped cap can be turned or not. A cap which does not turn indicates a good crimp.

Warning: this test is not very meaningful for two reasons:

  1. Many septa come with a PTFE lamination. Due to the smooth surface of the PTFE membrane, the cap can be turned even if the cap was crimped correctly.
  2. An overcrimped closure which passes the turning test will have impaired sealing characteristics due to the deformation of the cap and septa.

Take into account that resealing characteristics vary amongst septa and that repeat injections may cause coring and/or tearing of some septa. In general, septa made of silicone sandwich coated with PTFE, demonstrate excellent resealing characteristics. They are the product of choice for repeated injections and sample storage. Septa made of PTFE / rubber are a more economical solution for single injection applications that do not require long-term sample storage.

In general, crimp caps, which are attached or removed using crimping or decapping tools,
provide best quality seals for long-term sample storage. If you are looking for a convenient closure system that does not require additional tools, screw caps can offer a good compromise of secure fit and ease of use.

In contrast to crimp top and screw cap vials, snap cap vials are chosen strictly for convenience and for specific fill and finish equipment requiring nested snap cap configurations. Snap caps may be adequate for applications that do not require heating of the sample above room temperature and where moderate sealing performance can be tolerated.

The main function of the PTFE part of the liner is to create a nearly inert barrier between sample and septa material prior to injection. Therefore, this membrane always faces in the direction of the sample.

The hardness of a material is called durometer and measured in ° Shore. Different scales are used to specify what type of substance is described. For example, the “A” in “Shore A 45°” refers to the scale for flexible mold rubbers/plastic. Numbers go from 0 to 100. A high shore grade describes a hard liner whereas a low shore grade refers to a softer liner.