The one-line summary
If you need a hermetic, tamper-evident weld and you run an induction sealer, choose an induction seal liner. If you have no sealer and no budget for one, choose a pressure-sensitive liner and accept a non-hermetic seal. If you simply need a clean re-closable barrier for dry or low-risk fills, choose a foam or cap liner. Most wrong decisions come from picking by habit rather than by what the line and the product actually need.
How each one actually seals
Induction seal liners — heat-welded foil
An induction liner is a laminate with aluminium foil at its core. A sealing head above the capped bottle generates an electromagnetic field that heats the foil; the heat melts a heat seal lacquer onto the bottle mouth, and the weld sets on cooling. The result is a genuine foil-to-lip weld: hermetic, tamper-evident, and strong enough for liquids that travel far and sit on shelves for months. It requires an induction sealer on the line, so there is an equipment cost up front.
Pressure-sensitive liners — bond under torque
A pressure-sensitive liner is an adhesive-backed liner that bonds to the bottle mouth purely from the downward pressure of the cap being torqued on. There is no heat, no field and no machine. The trade-off is the seal: it grips rather than welds, so it is not hermetic in the same sense, and it is weaker against aggressive contents and rough handling. It suits simple lines and products that do not demand a foil barrier.
Foam and cap liners — compression seals
A foam liner is a resilient disc, typically EPE or LDPE foam, that compresses between the cap and the mouth to close the gap. It reseals cleanly every time the cap is reapplied, which makes it ideal for products that are opened and closed repeatedly. It is not a tamper-evident or hermetic barrier, so it is reserved for dry fills and low-risk liquids.
| Dimension | Induction | Pressure-sensitive | Foam / cap |
|---|---|---|---|
| Sealing principle | Foil heated by induction, heat seal lacquer welds to the mouth | Adhesive bonds under cap torque | Foam compresses between cap and mouth |
| Machine needed | Yes — induction sealer | No | No |
| Seal strength | Hermetic, tamper-evident weld | Grip seal, not hermetic | Re-closable, not hermetic |
| Equipment cost | Higher (sealer) | None | None |
| Contents fit | Liquids, oils, aggressive fills, long shelf life | Low-risk liquids, dry goods | Dry fills, repeated open-close |
| Typical barrier | Aluminium foil, 20 µm | Adhesive + film | Foam only |
Pros and cons, at a glance
Induction seal liners
- Pros: hermetic weld, strong tamper evidence, the best moisture and oxygen barrier, long shelf life, works on PE, PET, PP, PS, PVC, COEX and glass.
- Cons: needs an induction sealer, more line setup, and the cap and mouth have to be right for the weld to form.
Pressure-sensitive liners
- Pros: no machine, drops into an existing capping line, low entry cost, simple to run.
- Cons: a grip seal rather than a hermetic weld, weaker against oils and solvents, less tamper evidence.
Foam and cap liners
- Pros: clean re-closable seal, reusable, cheap, forgiving on mouth flatness.
- Cons: no hermetic barrier, no tamper evidence, limited to dry or low-risk fills.
Cost, not just unit price
Compare total cost, not the price per liner. An induction liner has a higher equipment entry cost — you need an induction sealer and the line space to fit it — but it protects higher-value fills and cuts leak-related returns. A pressure-sensitive or foam liner is cheaper to adopt because it drops into an existing capping line with no new machine, but it cannot do the job of a hermetic weld. If your product leaks or spoils, the "cheap" liner is the expensive one.
The maths changes once you price a failure. One returned pallet of leaked lubricant, one spoiled batch of food, or one customer who never reorders can cost more than an induction sealer costs to buy and install. When the contents are valuable and the consequence of a leak is severe, the "expensive" liner is the one that was never there to protect them. Compare the cost of the seal against the cost of a leak — not against the cost of the liner alone.
Which contents point to which liner
- Lubricants, agrochemicals, solvents, acids: induction. These demand a real barrier and tamper evidence.
- Personal care, household liquids, condiments: induction is the default; pressure-sensitive only if the line has no sealer and the risk is low.
- Dry tablets, powders, capsules: foam or pressure-sensitive is often enough; induction is over-engineering.
- Products opened and closed daily: a foam or cap liner, or a two-piece induction liner with a resealing backing ring.
Hybrids and edge cases
The three families are not always clean boxes. Several common structures borrow from more than one idea, and your product may sit in the overlap.
- Two-piece induction with a pulp or foam backing ring combines a hermetic foil weld with a re-closable backing that stays in the cap.
- Easy-open and pull-tab liners add a peel geometry to an induction or pressure-sensitive seal, so the consumer opens the pack in one piece without a tool.
- Vented liners weld a one-way membrane into the cap so gas can escape while liquid stays in — used for fills that build internal pressure.
If your product does not fit a clean category, tell us what it is and what it needs to survive. The answer is usually a hybrid, not a compromise.
How to decide without guessing
Answer three questions and the choice is usually obvious: Do you need a hermetic or tamper-evident seal? Do you already run an induction sealer? How aggressive is the contents? If you need hermetic and have a sealer, go induction. If you need hermetic and have no sealer, budget for one or downgrade the requirement deliberately. If you do not need hermetic, pressure-sensitive or foam will save you money.
When the answer is still not obvious, score the decision against this short list:
- Do you need a hermetic or tamper-evident seal, or just a closure?
- Do you already run an induction sealer, or can you budget for one?
- How aggressive is the contents — oils, solvents or acids?
- Is the pack opened and closed repeatedly, or single-use?
- What is the cost of a leak — returns, spoilage, brand damage?
A concrete example makes the trade-off clear. A lubricant bottle is filled on a line that already runs an induction sealer, and the product must survive two years on a shelf and shipping to a hot climate. Induction is the obvious answer — the foil weld is hermetic and tamper-evident, and the equipment is already paid for. The same bottle filled with dry bath salts, capped on a simple line with no sealer, points to foam or pressure-sensitive: no hermetic barrier is needed, and no new machine is worth buying for it.
Still unsure? Send us the container, the contents and your current capping setup, and we will recommend a structure — and send free sample liners in your diameter so you can prove it on your own line before you buy.