Aluminum cap, 38 mm

The 38 mm aluminium cap is a screw closure with a sealing insert for containers with a 38 mm neck finish. The soft expanded polyethylene (EPE) foam insert presses against the rim of the neck when tightened, sealing the container.

The cap is of cosmetic quality, making it suitable for closing containers with cosmetic products such as balms, butters, creams, oils or loose mixtures. It can also be used for technical formulations.

How the cap seals

The seal is not provided by the metal itself but by the EPE foam insert inside the cap. When screwed on, it compresses between the base of the cap and the neck rim, conforming to its shape and bridging minor surface irregularities. The insert also separates the contents from the metal. During normal upright storage, the contents therefore do not come into contact with the aluminium.

Do not remove the insert from the cap, as it will not seal without it. The aluminium shell is thin and lightweight, so it only needs to be tightened gently, just until the insert seats against the neck. Over-tightening can deform the thread and reduce the seal.

Suitable containers and contents

The cap fits containers with a 38 mm neck and a matching thread. Containers with the same neck type as well as ready-made container-and-closure combinations are available in the Handymade range. When using your own combination, we recommend checking that the cap threads on smoothly, that it seals properly and that the container behaves as expected with the specific formulation. The silver finish is neutral and pairs well with both glass and aluminium containers.

In terms of contents, the closure is particularly suitable for:

• Anhydrous products – balms, body butters and oil blends.
• Emulsions and water-based preparations – creams, gels or scrubs at the typical pH range of cosmetic products.
• Loose ingredients and blends – bath salts, clays and powder masks that need protection from ambient moisture.

What to know before use

Preparation before first use. Wipe or spray the cap, including the insert, with isopropyl alcohol (IPA) or ethanol and allow it to dry completely. Any moisture left under the insert or in the thread will enter the product once the container is closed.

Filling the container. The container should be filled to its nominal volume, meaning the volume it is designed for during normal filling. The total brim-full capacity is the physical volume up to the neck. The difference between the two provides headspace for the closure and for expansion of the contents when temperature changes. Filling right to the brim will force the contents into the thread and onto the insert when the cap is screwed on. Hot-fill products should be allowed to cool before closing to prevent moisture condensing under the cap.

Reuse. The condition of the insert is the deciding factor. It must be clean, resilient and undamaged. An insert that has absorbed the scent of a previous product is no longer suitable for a new one.

Handling and recycling. Thin aluminium dents easily on impact or under heavy pressure, so store the caps loosely, not under heavy loads. Aluminium is a recyclable metal; the sealing insert is made of plastic.

Frequently asked questions