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Views: 216 Author: Lumy Publish Time: 2026-11-09 Origin: Site
Content Menu
● Why induction sealing does not work with an aluminum cap
● The default workaround — and where it falls short
● A third option: embossed pure aluminum foil pressure sensitive liner
● One liner, two capping routes
● FAQ
● Work with a converter who understands the closure, not just the liner
Aluminum jars with matching aluminum caps are a familiar sight in skincare: horse oil balms, petroleum jelly, rich creams and ointments. The format looks substantial, feels cool in the hand, and gives a brand a clean all-metal presence on shelf. Yet one part of that package is usually decided by constraint rather than by design — the seal liner.
Because the cap is metal, the sealing technology most widely used across the industry cannot be applied here. That single constraint shapes everything downstream. This article sets out the constraint, the usual workaround and its limits, and a third option that many brand teams have not yet specified: an embossed pure aluminum foil pressure sensitive liner.
Induction sealing depends on an electromagnetic field passing through a plastic closure to heat the foil layer inside an induction seal liner and fuse it to the container rim. A metal cap changes that completely: the aluminum shields the field, so the liner inside never receives the energy it needs and the seal does not form.
For an all-aluminum jar-and-cap set, the practical options are therefore narrow. The pack either ships without a seal liner, or it uses a pressure sensitive liner — one that seals under the pressure of the closed cap, with no heat, no induction equipment and no electromagnetic field.
Terminology note: "induction liner" and "foil seal" are used loosely in some markets. Here, an induction seal liner means a heat-activated foil laminate; a pressure sensitive liner means a pressure-activated one. They are not interchangeable—a distinction worth settling before a specification is written.
The pressure sensitive liners in widest circulation are built on polystyrene (PS) foam. The foamed structure does two jobs at once: its thickness fills the gap between cap and jar rim, and it presses the pressure sensitive adhesive against the rim so the adhesive can form a barrier against oxygen and moisture vapour.
It works, and it is widely available. On an all-metal pack, though, it carries two visible drawbacks:
Aesthetic mismatch. A white foamed plastic disc is what the consumer sees when the cap comes off. Against an aluminum jar and cap, it reads as plastic and undercuts the premium, all-metal impression the format was chosen for.
Capping dependence. A PS foam liner generally needs a screw cap tightened onto the jar to generate and hold pressure, which constrains the closure design.
For a high-end balm or cream, the first point is not cosmetic nitpicking: the inside of the cap is part of the opening experience.
An embossed pure aluminum foil pressure sensitive liner starts from a thin pure aluminum foil — around 0.05 mm in the shop-floor phrasing of the original briefing ("five si"; gauge to be confirmed against the grade TDS). The foil is embossed, then coated with pressure sensitive adhesive to form the liner.
What changes is the face the consumer sees. When the cap is removed, the sealing membrane is aluminum — the same material, tone and light behaviour as the jar and cap. The pack reads as one coherent object rather than metal outside and plastic inside. For premium skincare, that consistency is often the whole reason the format was chosen.
The liner is also thin, so it lies flat against the entire rim of the jar, giving a clean, complete appearance with no bulky foam edge.
The less obvious advantage is that this liner is not tied to a screw cap. It can be specified with either a screw cap or a straight-sided press-on cap — by two different pressure mechanisms:
Screw cap | Straight-sided press-on cap | |
How pressure is applied | A PE foam insert inside the cap presses the liner onto the rim as the cap is turned down | The liner is cut slightly larger than the jar mouth; the cap pushes straight down and the overhanging edge is pressed across the rim, so the liner covers the mouth like a single sheet |
What must be specified | Cap must be supplied with the PE foam insert | Liner diameter relative to the jar mouth diameter |
PS foam pressure sensitive liner | The usual route: screw down to generate pressure | Not the route this construction is designed for |
Both routes produce the same sealing function: the adhesive is pressed against the rim and forms the barrier. Only the source of the compressive force changes — a foam insert inside the cap, or a cap pressing down on a slightly oversized disc.
That makes this a specification decision rather than a product change. One liner family can serve two closure designs, which is useful when a brand runs both a screw-cap and a press-on-cap SKU.
Conventional PS foam liners carry their markings as ink printed on the surface — "Sealed for your protection" being the most familiar. On the pure aluminum foil liner, the same message is raised by embossing rather than printed. The lettering catches the light together with the foil, a quieter and more integrated way to signal that the pack is sealed.
If a brand wants its own mark, the embossing can be produced as a custom logo. That requires a one-time embossing die; tooling terms should be requested together with the project specification. No figures are quoted here.
The pressure sensitive adhesive is the same type used on standard pressure sensitive liners and is formulated for applications where food contact is a requirement. On that basis, the construction is specified for:
Food and supplement packs
Cosmetics and skincare
Creams, balms and ointments — including horse oil and petroleum jelly formats
Aluminum jar / aluminum cap combinations generally
Compliance note: food-contact suitability, certificates and test reports are to be confirmed by Wanqi for the specific grade and target market. No certification status is claimed in this article.
An all-foil liner is materially closer to the metal pack it sits in than a foamed plastic disc, and that can support the recyclability of the overall package. This is a qualitative consideration, not a measured claim: actual recovery depends on local collection and sorting streams, on whether the liner is removed at end of life, and on the adhesive system in use. No recycling rate has been quantified here.
Before sampling, five points are worth settling with your supplier:
1. Closure type — screw cap or straight-sided press-on cap. It determines where the pressure comes from.
2. If screw cap — confirm the cap is supplied with a PE foam insert. Without it, the thin foil liner has nothing to press it against the rim.
3. If press-on cap — specify the liner diameter against the jar mouth; it needs to be slightly oversized.
4. Markings — standard embossed "Sealed for your protection", or a custom embossed logo (tooling required).
5. Regulatory scope — confirm food-contact documentation and any market-specific requirements for the grade you are buying.
Why can't I use an induction seal liner with an aluminum cap?
The metal cap shields the electromagnetic field that induction sealing needs to heat the foil layer. Without that energy the liner does not fuse to the rim. Induction sealing is normally paired with plastic closures.
Does a pure aluminum foil pressure sensitive liner need a screw cap?
No. With a screw cap, a PE foam insert inside the cap supplies the pressure. With a straight-sided press-on cap, a slightly oversized liner is pressed down vertically across the mouth instead.
Can the embossed marking be customised?
Yes — the embossing can be produced as a brand logo. A one-time embossing die is required; request tooling terms for your project.
Is it suitable for food and cosmetic products?
The adhesive is the same type used on standard pressure sensitive liners and is formulated for food-contact applications. Confirm the documentation for your grade and target market before release.
Does it contain a wax bonding layer?
The construction described here is pure aluminum foil plus pressure sensitive adhesive — there is no paperboard or wax bonding layer. Confirm the full layer stack on the TDS for the grade supplied.
At Wanqi, we build our laminating and die-cutting processes around how these materials behave against real closures — the cap insert, the rim tolerance, the embossing depth. If you are qualifying a seal for an aluminum jar, send us the cap type, mouth diameter and marking requirement. We will recommend a construction and provide samples for line trials.
Technical note: foil gauge "five si" is an oral shop-floor expression interpreted here as approximately 0.05 mm; confirm against the grade TDS. The market options, product applications and recyclability remarks above are qualitative statements from the source briefing, not a market survey or measured data. No price, MOQ, lead time or certification status is stated in this article.
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