Quick answer: Induction foil liners, hot melt adhesive liners, foam liners and pressure sensitive liners are four different sealing methods, not four grades of the same product. Induction liners weld to the bottle rim and require an induction sealing machine. Hot melt, foam and pressure sensitive liners are applied by the closure itself and seal on torque and contact pressure. Choosing between them is a decision about your filling line and your customer's opening experience, not about price.
Most packaging specifications that go wrong at Hangzhou Xinxing Pharmaceutical Packaging go wrong on the same point: the liner type is treated as a purchasing decision when it is actually a filling-line decision. The four liner families below are distinguished by how the seal is created, and that determines what equipment is needed, what the end user experiences on opening, and what quality controls apply.
How each liner type creates its seal
| Liner type | How the seal forms | Extra machine required | Recloseable after opening |
|---|---|---|---|
| Induction foil liner | Aluminium foil is heated by an electromagnetic field; the sealant film melts and welds to the container rim | Yes — induction sealing head | No — one-trip seal, destroyed on removal |
| Hot melt adhesive liner | Pre-applied adhesive bonds to the rim under the torque and head pressure of the capping machine | No | No — clean peel, single use |
| Foam liner (HDPE / LDPE / EPE) | Compressible foam is held against the rim by cap torque; sealing is mechanical, not adhesive | No | Yes — reseals each time the cap is replaced |
| Pressure sensitive liner | A pressure-sensitive adhesive coating bonds to the rim when the cap is torqued down | No | No — peel once and discard |
The first row is the only one that requires capital equipment. That single fact eliminates induction liners from a large share of packaging lines before any product consideration enters the discussion.
When induction sealing is the correct answer
Induction foil liners are the right choice when all three of the following are true:
- The product needs a hermetic, tamper-evident seal. A welded foil seal is a continuous bond around the entire rim. It provides a barrier against moisture, oxygen and contamination that no contact seal can match, and it cannot be removed and reapplied without visible damage.
- The line already has, or can justify, an induction sealer. This is the decisive constraint. The equipment must be installed downstream of the capper and tuned to the specific container, closure and line speed.
- The product justifies the seal. Pharmaceutical dosage forms, nutraceuticals, agrochemicals and any product where a leak or an unnoticed opening carries regulatory or safety consequences.
Induction sealing also has the broadest material range. Because the sealant film is selected independently of the foil, a PP, PE, PET or multi-layer film can be chosen to match the container plastic and the product chemistry. This is why the same induction liner platform serves pharmaceutical bottles, plastic food containers and chemical oil drums.
When the other three types are the correct answer
Hot melt adhesive liners suit lines without induction equipment that still need a clean, tamper-evident seal. Because the adhesive is pre-applied to the liner and activated by the capping machine's own torque and head pressure, no separate sealing step exists. The trade-off is that the bond depends on consistent capping torque — a capper with variable torque will produce a variable seal.
Foam liners are the choice when the end user must be able to reopen and reseal the container repeatedly. The foam is compressed by the cap and springs back against the rim each time it is closed. This makes foam the standard for products dispensed over multiple uses where a one-trip seal would be inconvenient. HDPE foam, LDPE foam and EPE foam differ in density, compressibility and chemical resistance, and the choice follows the product and the required resealing force.
Pressure sensitive liners are used where a peel-away seal is wanted without induction equipment. The adhesive bonds on contact under capping torque, giving a seal that opens with a controlled peel force. They are common on cosmetic and personal care containers where the seal is a hygiene and tamper indicator rather than a barrier requirement.
The line-capability decision tree
| Question | If yes | If no |
|---|---|---|
| Is an induction sealer installed and tuned? | Induction foil liner is available | Exclude induction; continue below |
| Must the seal be hermetic and tamper-evident? | Hot melt adhesive liner or pressure sensitive liner | Continue below |
| Must the container be recloseable many times? | Foam liner | Hot melt adhesive liner |
| Is the closure torque consistent across the batch? | Hot melt or pressure sensitive works reliably | Foam liner — mechanical seal tolerates torque variation better |
The last row is the one most often overlooked. Adhesive-based seals are torque-dependent by design; a container sealed in a capper with ±30% torque variation will show a corresponding spread in seal performance. A compressible foam liner is mechanical and is considerably more forgiving of that variation. If the capper is the constraint, foam may be the more reliable production answer even where an adhesive seal would be technically superior on paper.
Peel behaviour is a specification, not a detail
For the one-trip seal types, how the seal opens is a specified property:
- Peelable — the foil lifts off progressively in one piece. Standard for consumer products and for pharmacy dispensing.
- Weld / clean peel — the film separates from the foil so the film remains bonded to the rim, with no fibre tear. Common where the container is reused or where residue on the rim is unacceptable.
- Tamper-evident with visible lift — the seal separates in a way that makes interference obvious.
A liner specified only by type and dimensions leaves peel behaviour undefined, and two suppliers can deliver the same nominal product with different opening characteristics. This is a specification gap that shows up in customer complaints before it shows up in any incoming inspection.
Frequently asked questions
Can a foam liner be used on pharmaceutical products?
It depends on the product and the regulatory classification. A foam liner is a mechanical seal, not a hermetic one, so it is generally unsuitable where a moisture or oxygen barrier is required. For products where resealability matters more than barrier, foam is appropriate and is widely used in pharmaceutical and food packaging.
Do I need to buy an induction sealing machine to use foil liners?
Yes. An induction liner contains no adhesive; the seal is created by the sealing machine heating the foil. Without an induction sealer, a foil liner will not seal at all, although it will still sit in the cap as a loose insert.
Which liner type gives the strongest seal?
A welded induction foil seal. It is a continuous bond around the entire rim and provides barrier and tamper evidence that contact-based seals cannot match. "Strongest" in the sense of reclosability is a different question, and there a foam liner wins.
Can I switch liner types without changing my capping machine?
Usually yes, provided the liner thickness is compatible with the cap and the torque settings are re-validated. Foam liners are thicker than foil liners, so the cap depth and the applied torque may need adjustment.
Do you supply all four liner types?
Yes. Hangzhou Xinxing Pharmaceutical Packaging manufactures induction foil liners, hot melt adhesive liners, HDPE and LDPE foam liners, and pressure sensitive liners, and can recommend the suitable type from the filling line capabilities and the product requirements.
Start from the line, not the catalogue
Tell us whether an induction sealer is installed, how consistent your capper torque is, and what the end user needs to be able to do after opening. Those three answers narrow the choice to one or two liner types immediately. Our engineering team has been supporting pharmaceutical, cosmetic and food packaging customers from our Tonglu, Hangzhou facility since 2001, and can supply samples of all four types for line trial.