Liner Notes
How Tamper-Evident Seals Work (and How to Pick the Right One for Your Product)
A tamper-evident seal is designed to leave visible evidence when the package is opened: through a VOID message, a torn or fragmented facestock, a broken perforation, or another irreversible-looking change. Its job is to make opening harder to hide, not to make the package impossible to enter.
The same seal can pass or fail depending on what it's stuck to. A void label on a dry glass jar splits exactly as designed when someone lifts it. On a cold, sweating high-density polyethylene bottle, that same label can peel off whole and leave nothing behind.
Four things decide which result you get: the adhesive, the surface, the seam the seal bridges, and the conditions on your line and in storage. Liberty produces the anti-tamper and security versions of pressure-sensitive labels.
Issues with seals for these labels typically trace back to a mismatch between adhesive, surface and line. Testing on your own containers is how you find out which one you have.
A tamper-evident seal shows the opening, while tamper-resistant packaging slows it
Does a seal stop someone opening the package? No. Under Title 21 of the Code of Federal Regulations, section 211.132 (21 CFR 211.132), the FDA rule for over-the-counter drug packaging, a tamper-evident package is "one having one or more indicators or barriers to entry which, if breached or missing, can reasonably be expected to provide visible evidence to consumers that tampering has occurred."
Tamper-resistant packaging works on a different problem by making the package harder to open, the way a child-resistant closure or a blister pack does. Many packages use both.
Is anything actually tamper proof? No seal prevents a determined opening, so read "tamper proof" as everyday shorthand for tamper evident, the standard over-the-counter drugs have been held to since the 1982 Tylenol poisonings in Chicago. The more useful questions are what evidence the seal leaves and who will be there to see it.
Tamperseal, security seal, VOID sticker: which is which? "Tamper seal" and "tamperseal" are informal names that usually mean a pressure-sensitive label over a closure.
A "security seal label" is a label with void, destructible or serialized features built in. "Tamper evident stickers" are usually void or destructible labels sold in small packs, and "tamper evident tape" is void film on a roll for carton flaps.
Void film, destructible faces, security cuts and printed patterns each leave different evidence
Each of these label constructions shows an opening in its own way, and each has a known weak spot.
Void residue and non-residue film
A void label has a hidden layer inside it, printed in a pattern, that bonds more weakly than the adhesive holding the label to the package. Lift the label and it splits at that weak layer.
On the residue version, VOID or a custom pattern stays behind on the surface. On the non-residue version, the message shows only in the lifted label, which suits electronics housings and returnable totes where you don't want the product itself marked.
Heat exposure can alter adhesive behavior, so a seal that relies on splitting or tearing in a particular way should be validated across the temperatures it may encounter in real use. A heated adhesive softens and can let go before the hidden layer splits, so the label comes up intact.
The residue version holds up better here, because a label pressed back down won't line up with whatever was left on the surface, and an adhesive matched to the substrate makes a warmed peel harder to pull off. Void film fits cartons, cases and housings.
Destructible (frangible) facestock
A destructible face, sometimes called frangible, is a facestock that's weaker than its bond to the surface, so it breaks into fragments when someone tries to lift it. A patient, slow peel on a smooth surface can sometimes bring one up in larger pieces, and a solvent can loosen the adhesive underneath.
Security cuts and an aggressive permanent adhesive make both approaches harder. These faces suit caps, small containers and asset tags, though they can be fragile on some automatic applicators, so tell your supplier how the labels will go on.
Perforations, slits and kiss cuts
Cuts turn a lift into a tear. Perforations, slits and kiss cuts (shallow cuts through the face only) give the label weak lines that tear when it's flexed or lifted, and that fray visibly if someone slices along a seam with a knife. They're often paired with a destructible face and fit carton tuck flaps and strips that run from cap to neck.
The cut has to be held accurately, or the seal tears early on the line or not at all when opened. That's why Liberty checks die-cut accuracy in-process.
Printed patterns and serial numbers
Some evidence shows up by comparison. A replacement label doesn't match the brand pattern, or its number doesn't match the log.
The FDA rule asks for a package that is "distinctive by design" or that uses an indicator with "an identifying characteristic (e.g., a pattern, name, registered trademark, logo, or picture)." Liberty can print a brand-specific pattern through flexographic label printing with spot color matching, and your regulatory team decides whether that pattern meets your requirement.
For some shipping-carton applications, a stock VOID construction may provide the level of visible evidence the program requires. A custom pattern earns its cost when replica labels are a realistic threat.
Serial numbers work the same way, through variable data printed on each seal. They help only if someone records the number and checks it at receiving or on the returns desk. A serialized seal nobody checks is decoration you paid for.
Shrink bands, induction liners and breakaway caps belong to your closure supplier
Some of the best tamper evidence for a bottle or jar isn't a label at all. These seal types come from film, closure or packaging suppliers, and for a supplement or food bottle one of them is often the right primary barrier.
- Shrink bands: heat-shrunk film over the cap and neck, usually with a perforated tear strip that has to come off before the cap turns.
- Induction liners: a foil liner bonded to the container rim at capping, which can't be resealed once it's peeled.
- Breakaway caps and tear bands: a ring molded into the closure that snaps off the first time the cap is twisted.
- Tamper-evident tape: void film on a roll, run across carton flaps.
- Tamper-evident bags: bags with an irreversible adhesive closure, used for evidence, cash and returns.
Many bottles run a closure feature and a label together. A label can be sized and matched to the closure you already use, giving you a second visible indicator that carries your brand.
Tamper-evident labeling earns its place on bottles, tubs, cartons and kits
Food and beverage closures. Lids and caps here sit in cold, wet, condensing conditions, so the seal runs cap-over-neck or lid-to-tub on an adhesive that holds through the cooler and the freezer.
Supplement bottles. A supplement bottle usually carries an induction liner under the cap and a printed seal over it.
Retailers and marketplaces often expect visible tamper evidence on these products, and the seal label is the part a shopper sees before the bottle is ever opened. Liberty prints seals alongside its supplement and nutraceutical labels, matched to the same bottle.
E-commerce cartons. A void label across the flaps shows evidence at the receiving dock or on the customer's doorstep.
Medical and lab kits. Kits stored refrigerated, frozen or at cryogenic temperatures need an adhesive rated for that range, and many carry serialized seals tied to lot traceability. Liberty supplies the label construction, and the kit maker owns its compliance.
Consumer electronics returns. Non-residue void labels over box openings or housings let a returns desk see whether a unit was opened before it came back. The seal is only as good as the person checking it, and a void label on a box nobody inspects changes nothing.
Bridge the part that moves, or the seal records nothing
Twist a cap with a seal sitting only on its top, and the seal rides along with the cap, undisturbed. Run that seal from the cap down onto the neck or shoulder, and the same twist forces it to tear. Every placement rule follows from that, because the seal has to cross the line where two parts separate.
On bottles and jars, run the seal from the cap onto the neck or shoulder. Small diameters and ribbed caps are where edges start to lift, so give the label enough length on each side to hold.
On a folding carton, bridge the tuck flap and the panel it closes onto. A common miss is a seal across a glued seam that never opens. It records nothing, and placement errors like that produce more useless seals than any material choice.
Shipping cartons and poly mailers get sealed across the closure itself, flap to body.
For clamshells and kit lids, cross the lid-to-tray seam on the side a person would pry first.
Wherever it goes, the seal needs a clean, dry surface at application temperature and firm pressure across its whole area. Then give the adhesive time to build its bond before the package is stacked, shipped or squeezed. Mark the seal position on a sample, open the package the way a customer would, and watch whether it breaks.
Eight questions about your container and line pick the construction
These are the questions we ask before quoting a seal, and most of them can be answered from the plant floor in an afternoon.
- What's the container made of? Polyethylene and polypropylene, the plastics behind most squeeze bottles, tubs and caps, have low surface energy. Liquids bead on them the way rain beads on a freshly waxed car hood, and many adhesives behave the same way, sitting on top of the plastic instead of flowing into it. Clean, smooth glass is generally easier to bond than many low-surface-energy plastics. Coated or varnished cartons vary from job to job.
- What's the shape? Diameter, ribs, flanges and texture all change how a seal sits and where it lifts.
- How cold does it get in storage? Refrigerated, frozen and ultra-cold storage each call for a different adhesive, and cryogenic adhesive is available for lab and biotech kits.
- Does it sweat on the line? Containers filled or chilled cold pick up condensation right where the seal goes.
- Hand or automatic application? Destructible faces may not suit every applicator. Tell your label supplier which applicator you run so the roll is wound for it. Liberty finishes in rolls, sheets and continuous fanfold.
- Does a second attempt need to show? If a seal that's peeled and pressed back down must still give itself away, use a residue construction or serialization.
- Who checks the evidence? A receiving dock, a returns desk and a consumer each look for different things, so the seal should be readable by whoever is actually looking.
- What's driving the request? A regulation, a retailer requirement and a returns report each lead to a different spec, and the regulatory side is covered in the questions further down.
Storage range and applicator type are worth answering early. Together, they often determine whether a destructible face suits the line.
Most clean peels trace back to adhesive, surface or line conditions
A seal goes onto a chilled polyethylene bottle at the end of a humid line. It looks perfect in the case.
By the next morning in the cooler, one edge has lifted. Someone tugs it, and the whole label comes away in one piece with no VOID left behind.
Nothing was wrong with the facestock.
The adhesive never wet out the low surface energy plastic, so it was holding on through a fraction of its contact area. Cold stiffened it further, and a thin film of condensation trapped at application sat between the adhesive and the bottle.
Dust, product residue or a wet flange do the same thing, because the adhesive bonds to the contamination instead of the container. Textured, silicone-containing and nonstick polytetrafluoroethylene (PTFE) surfaces limit adhesion too.
Heat can work in the opposite direction from cold by softening some adhesive systems. If the adhesive releases before the security layer activates, the seal may lift more cleanly than intended. That is another reason to validate the complete construction across the temperatures it may encounter.
The reverse problem causes its own complaints. A destructible face that fractures on the applicator or in normal handling creates false evidence, and a customer who finds a torn seal on an untouched bottle will call it tampering. That's a construction too fragile for the line, and it shows up in testing long before it shows up in returns.
Run a small pilot lot on your own containers before you commit
Start by gathering empty production containers and writing down the fill temperature, line conditions and storage range. Choose two or three candidate constructions with your label supplier.
Apply them exactly as production will, with the same applicator or hand method at the same line temperature. Then condition the samples in the cooler, the freezer, or a trial shipment that goes out and comes back.
Challenge the samples using the kinds of handling, temperature variation, peeling, and mechanical stress they could reasonably encounter in the field. Confirm that intended opening creates visible evidence while normal handling does not.
Liberty has no minimum order quantity, so a validation lot of a few dozen seals is practical. Adhesion and die-cut accuracy are inspected in-process, and we retain job specifications and physical samples from each run, so the production order matches the pilot that passed. Lead times are competitive, and the team regularly accommodates rush requests.
A spec sheet can't tell you how a seal behaves on your bottle in your freezer. A short pilot can reveal problems that a datasheet cannot.
What quality and regulatory teams ask about tamper seals
Which tamper-evident seal is best for my package?
It depends on the container surface, closure geometry, storage conditions, application method, and the kind of evidence you want the user to see. VOID films, destructible facestocks, security cuts, and serialized constructions each behave differently.
Where should a tamper-evident seal be placed?
It has to bridge the opening line, the point where two parts separate. On a bottle, that usually means cap-to-neck; on a carton, flap-to-panel.
Can a tamper-evident label work on cold or wet containers?
Potentially, but adhesive selection and surface condition become critical. Condensation, low-surface-energy plastics, and cold application can all interfere with proper bonding, so the actual package and application conditions should be tested.
Can I add tamper evidence without redesigning the package?
Often, yes. A seal label can bridge the closure and existing container, provided the adhesive, dimensions, and placement are matched to the package.
Does an intact tamper seal prove the product is authentic?
No. An intact seal indicates that the closure does not show the expected signs of disturbance. Product authentication is a separate control.
What does the FDA require for over-the-counter tamper-evident packaging?
Most OTC drug products sold at retail must use tamper-evident packaging under 21 CFR 211.132, with certain product-specific exceptions. The regulation also requires labeling that identifies the tamper-evident feature. Your regulatory team should determine how the rule applies to your product; Liberty’s role is to provide a label construction that supports the approved packaging design.
Do supplements need tamper-evident seals?
Check with your regulatory team, because 21 CFR 211.132 is written for over-the-counter drug products and dietary supplements fall under separate rules. Tamper evidence is also commonly used on dietary supplements, and some retailers or marketplaces may impose their own requirements.
Seal a dozen containers tonight, then tell us what you find
Pull a dozen empty containers off the line, seal them the way production would, store them where the product lives, and try to peel one in the morning.
If the seal comes off clean, or you want to compare constructions side by side, send us the container, its fill and storage conditions, and how the labels will be applied. We'll suggest constructions and run a pilot lot. You'll work directly with the people specifying and printing the job, at a company that's been independently owned since 1969.