Pick the Right Induction Seal Liner for Your Bottle

Start with the bottle mouth, not the liner

The single rule that determines whether an induction seal holds is material matching. During induction sealing, a coil above the cap generates a field that heats the aluminium foil inside the liner. That heat melts a heat seal lacquer against the bottle lip, and the weld sets on cooling. If the lacquer is not from the same polymer family as the mouth, there is nothing to weld to — the liner simply will not bond, no matter how much power the line applies.

That is why we start every conversation with the container. Tell us the bottle material and the mouth diameter first, and the rest of the structure follows. The liner is engineered to the bottle, never picked off a shelf in the hope that it fits.

The bottle mouth materials we match

An induction liner works on thermoplastics and on glass. In practice that covers polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), PVC, multi-layer co-extruded (COEX) mouths, and glass jars. Each takes a different heat seal grade, because each polymer melts and welds at its own temperature window and has its own surface energy.

The table below is the quick map. It is a starting point, not a substitute for a sample trial: two "PE" bottles can still behave differently because of additives, colourants or how flat the lip is moulded.

Contents decide the barrier and the seal

The contents decide the barrier and the seal grade, because two fills with the same bottle can need different liners. Oils, solvents and acids demand a more resistant structure than water, while dry powders and tablets often need only a tamper-evident seal.

• Oils and solvents attack some seal layers and adhesives. A liner that is perfect for water may soften or lift against a solvent-based product, so the seal grade and any bonding layer are chosen for resistance.
• Acids and aggressive chemicals push you toward a higher-barrier structure, often with a heavier foil or a resistant coating, rather than a basic build.
• Food, personal care and pharmaceutical fills add hygiene requirements. These liners are produced under GMP-organised conditions, in our Class-100,000 clean room, with every batch checked in our own laboratory before dispatch.
• Dry powders and tablets rarely need a hermetic foil weld; they may only need a tamper-evident seal or a simple re-closable liner.

If you are unsure how aggressive your fill is, send us the safety data sheet (SDS) and we will read the chemistry for you. It is cheaper than guessing wrong.

Three sealing methods, one decision

Induction, pressure-sensitive and foam liners are the three mainstream closure types, and each solves a different problem. Induction gives a hermetic, tamper-evident foil weld; pressure-sensitive bonds under cap torque with no machine; foam re-closes cleanly for dry or low-risk fills.

• Induction seal liners need an induction sealer. They give a hermetic, tamper-evident foil weld and are the strongest barrier of the three.
• Pressure-sensitive liners bond under cap torque alone — no machine, no heat. They are easier on simple lines but offer a weaker, non-hermetic seal.
• Foam and cap liners are compression seals that re-close cleanly and suit dry or low-risk fills.

We compare the three in detail in Guide 02: Induction, Pressure-Sensitive or Foam. The short version: if you need a hermetic weld and you have an induction sealer, induction is the answer; if you have no sealer and no budget for one, pressure-sensitive or foam is the pragmatic choice.

Cap torque and mouth flatness

Cap torque and mouth flatness decide whether a correctly matched liner actually seals, because the cap must press the foil flat against a flat lip for the weld to form. Too little torque leaves the foil off-square, and an uneven lip leaves gaps where the weld cannot form.

• Cap torque. The cap has to press the liner flat against the mouth during sealing, then hold it there. Too little torque and the foil does not sit square; too much and the liner can be crushed or the cap over-tightened.
• Mouth flatness. The bottle lip must be flat and free of flash or sink marks. An uneven lip leaves gaps where the weld cannot form, which is the classic cause of "looks sealed but leaks".

If your mouth is non-standard, send a photo or drawing. We configure the backing and the seal layer around the lip profile, and we validate the result on sample liners before you commit to a production run.

One-piece or two-piece?

The first build decision is whether the liner separates into two pieces on opening or lifts off in one, because this controls resealing. A two-piece liner keeps a paperboard backing ring in the cap for resealing, while a one-piece liner lifts clean off for single-serve or dry packs.

• Two-piece is the classic liquid build. The foil membrane welds to the bottle as tamper evidence, while the paperboard backing ring stays in the cap so the pack reseals every time it is closed.
• One-piece lifts off the mouth in a single piece, leaving nothing in the cap. It is cleaner for single-serve packs and dry fills where resealing is not needed.

If your product is opened and closed again — lubricants, syrups, household chemicals — two-piece is usually right. If it is opened once and finished, one-piece gives a tidier finish. The decision changes only the backing and the release wax, not the barrier foil.

The four layers, configured for you

Every induction liner is a four-layer laminate of paperboard backing, release wax, 20 µm aluminium foil and heat seal lacquer, because each layer has a distinct job. The foil is the barrier the induction field heats, while the lacquer is the layer matched to your bottle polymer.

1. Paperboard backing. A stiff pulp ring (in two-piece builds) that stays in the cap for resealing, or a thin backing that peels away (one-piece). It carries the print and gives the liner body.
2. Release wax. A thin wax layer that lets the foil membrane separate cleanly from the backing when the cap is opened.
3. Aluminium foil, 20 µm. The active barrier and the layer the induction field heats. It is what makes the seal hermetic and tamper-evident.
4. Heat seal lacquer. The layer that melts onto the bottle mouth. This is the layer we match to your polymer — it is the whole point of the exercise.

Those four layers are laminated in-house at our Shanghai plant, then die-cut to any diameter in the Ø 9–182 mm range. Nothing is outsourced, which is how we keep the structure you approve consistent from sample to mass production.

Common mistakes to avoid

The three most common specification mistakes are choosing a liner by habit instead of by polymer, ignoring the bottle mouth, and specifying the foil but not the backing, because all three are made before a sample is ever sealed.

• Choosing by habit, not by polymer. A liner that worked on a PE bottle will not necessarily weld to a PET bottle. Match the seal layer to the mouth every time.
• Ignoring the mouth. The best liner in the world cannot weld to a warped or flashed lip. Check flatness before you blame the liner.
• Specifying the foil but not the backing. The barrier is only half the structure. The backing decides how the liner sits in the cap and how it opens.

Send us the container and the contents and we will flag any of these before they cost you a production run.

How to short-circuit the whole decision

You do not have to work this out alone. Send four things — the container material, the mouth diameter, the cap type and the contents — and we reply within 48 hours with a proposed layer build-up and a free sample plan. Sample liners in your diameter are free; you cover only the courier cost.

See the full product family and its variants on the induction seal liners page, or ask a question on the FAQ.