Liners, Seals & Tamper Evidence
A properly selected cap is important, but some packages need additional components to help create a secure seal, prevent leakage, or provide evidence that a package has been opened.
These components may include cap liners, induction seals, tamper-evident bands, and other packaging features.
In this lesson, we'll introduce these common options and explain their different functions.
A cap liner is a material or component positioned inside certain closures.
Depending on its design, it may compress against the container's sealing surface, help limit leakage, improve product protection, or be used to create an inner seal.
Not every closure requires a separate liner. Some use linerless sealing designs.
A cap liner and a tamper-evident feature do not necessarily serve the same purpose.
The correct combination depends on the product, closure, container, and application.
Common Types of Cap Liners
Liners come in different materials and constructions. Each is designed for particular packaging needs.
Foam Liner
A foam liner is designed to compress against the container's sealing surface when the cap is applied.
Purpose: Depending on the design, it may help create a seal and reduce leakage.
Remember: A typical foam liner is not automatically tamper-evident.
Pressure-Sensitive Liner
Certain pressure-sensitive liners adhere to the container opening when appropriate pressure is applied.
Purpose: They may provide a removable inner seal for suitable products and containers.
Remember: These are not interchangeable with induction seals and should not automatically be considered leakproof.
Induction Seal Liner
A foil-based liner designed to bond to the container opening through a controlled induction-sealing process.
Purpose: A properly designed and applied seal can provide leak resistance, product protection, and tamper evidence.
Foam, pressure-sensitive, and induction liners use different sealing approaches.
Liner selection must consider product compatibility, container material, neck finish, sealing equipment, and intended performance.
What About Linerless Closures?
Some closures are engineered to seal against a compatible container without a separate inserted liner.
These are commonly called linerless closures.
Their performance still depends on the container, closure design, product, and application.
Understanding Induction Sealing
Induction sealing is a common method of creating an inner seal across the opening of certain bottles and jars.
Induction sealing uses a controlled electromagnetic field to heat the foil layer of a compatible liner inside the applied cap.
Heat activates the liner's sealing material, allowing it to bond to a compatible container opening.
After cooling, the bonded liner forms an inner seal.
Four Basic Steps
The product is filled into the selected bottle or jar.
The cap containing the appropriate liner is applied.
The induction equipment heats the liner's foil and activates its sealing layer.
The compatible liner bonds to the container opening as the seal cools.
Where Might You See an Induction Seal?
Think about a container with a foil-like membrane across its opening beneath the screw cap.
The membrane may need to be peeled away or punctured before using the product.
This is a familiar example of an inner-sealed package.
Induction sealing is one method used to create this kind of package.
An induction liner cannot simply be selected based on cap size alone.
The liner construction, container material, sealing surface, closure, application torque, and sealing equipment must be compatible.
Actual seal quality must be evaluated and verified.
Understanding Tamper-Evident Packaging
Tamper-evident features are designed to make evidence of opening or interference visible to the user.
Tamper-evident packaging includes one or more indicators or barriers intended to provide visible evidence if the package has been opened or interfered with.
These features do not guarantee that tampering cannot occur.
Breakaway Band
A band designed to separate or break when the closure is first opened.
Example: Certain beverage and specialty packaging closures.
Shrink Band
A band or sleeve applied around the closure area.
It is designed to show visible evidence when removed or broken, depending on its design.
Tamper-Evident Inner Seal
A bonded membrane over the container opening that can provide visible evidence of removal or disturbance.
Proper design and sealing are essential to its function.
Tamper-evident: Intended to show visible evidence of opening or interference.
Child-resistant: Designed and tested to make opening difficult for young children.
A tamper-evident feature does not automatically provide child resistance.
Do All Products Require Tamper-Evident Packaging?
Requirements depend on the product, market, applicable regulations, and customer specifications.
Certain regulated products have specific tamper-evident packaging requirements.
For example, many over-the-counter drug products sold in U.S. retail settings are subject to tamper-evident packaging requirements under applicable FDA rules.
The appropriate requirements should be verified for the particular product and market.
How Do You Choose a Liner or Seal?
Selecting a liner or sealing method begins with understanding the product and the complete package.
Six Important Questions
- What product is being packaged? The formulation can affect material and liner compatibility.
- What bottle and cap will be used? Confirm the neck finish, container material, and closure design.
- What sealing performance is needed? Is the goal leak resistance, an inner barrier, tamper evidence, or a combination?
- What filling and sealing equipment is available? Different sealing systems have different process needs.
- Are special requirements involved? Consider shelf life, shipping, consumer use, and applicable regulations.
- Has the combination been tested? Verify product compatibility, seal integrity, and functional performance.
Real-World Packaging Examples
Example 1: A Nutraceutical Bottle
A company is packaging capsules in a wide-mouth plastic bottle.
The project may require a closure with an inner seal to meet the customer's product protection and packaging requirements.
An induction seal may be considered if it is suitable for the container, product, closure, and filling process.
Example 2: A Household Liquid Cleaner
A customer is experiencing leakage during transportation.
It may be tempting to simply choose a different cap liner.
However, the concern could involve the bottle's sealing surface, cap fit, liner, product compatibility, capping process, or shipping conditions.
The takeaway: Investigate the complete package rather than assuming the liner is the cause.
Example 3: A Personal Care Product
A brand wants consumers to see whether a bottle has been opened before purchase.
Depending on the product and package, a suitable tamper-evident band or inner seal may be considered.
The final solution should meet the customer's requirements and any applicable regulations.
Ask: "What do you need the seal to accomplish?"
Prevent leakage? Provide visible opening evidence? Help protect product quality? Meet a specific packaging requirement?
Understanding the goal is the first step toward evaluating the right option.
What You've Learned
Liners, seals, and tamper-evident features help support different packaging requirements.
Six Things to Remember
- A cap liner is a component inside certain closures that helps provide sealing or other functions.
- Foam liners can help create a seal through compression.
- Pressure-sensitive liners and induction seals use different sealing methods.
- Induction sealing can bond an inner liner to a compatible container opening.
- Tamper-evident features are intended to provide visible evidence of opening or interference.
- The complete package must be evaluated for compatibility, sealing performance, and applicable requirements.
You've completed the three lessons in Closures & Functionality:
Lesson 9 — Understanding Neck Finishes
Lesson 10 — Caps, Closures & Dispensing Systems
Lesson 11 — Liners, Seals & Tamper Evidence
Our next activity is a five-question interactive Knowledge Check covering neck finishes, dispensing systems, liners, and tamper-evident packaging.