Pressure Sensitive Liners vs. Heat Induction Liners

When it comes to sealing containers, it is important to know the qualities of cap liners. Pressure sensitive liners and heat induction liners are both popular options that minimize leaks and contamination while helping maintain product quality. However, not all liners are universal. Some cap liners are suited for certain items based on their consistency, duration of use, and more. Identifying these traits will allow you to match your products with the optimal bottle, cap, and liner.

A pressure sensitive liner is a cap liner with a torque activated coating applied to one side. This adhesive coating is designed to stick to the rim of a container, firmly sealing the contents inside. The liner will remain sealed to the top of the container even when the cap is removed. Our selection of pressure sensitive liner sizes range from 15mm to 120mm, making them compatible with various bottles, jars, and containers. 

To work properly, pressure sensitive liners must be placed inside of the bottle cap. When the cap is screwed on and pressure is applied to it and the liner, the adhesive becomes activated and creates the seal. Leaving the cap in place for at least 24 hours is recommended, as this allows the liner to fully fasten itself to the bottle.

Foil pressure sensitive liners have several layers. They consist of polystyrene foam and an aluminum foil inner seal, which is coated on one side with the adhesive that sticks to the bottle. 

Eco-friendly liners are crafted from virgin pulp and kraft materials. They serve the same purpose as foil seals, but provide a more earth-friendly option. These liners are biodegradable, meaning they will naturally decompose if discarded in the trash.

Pressure sensitive liners provide several benefits to a bottle’s contents. Their primary function is to prevent leakage and product loss in coordination with bottle caps. If the primary closure is loosened or removed, the cap liner will remain on the bottle until its contents are ready to be used. Since the seal is airtight, they also prevent contact with oxygen and other gases to prolong product freshness.

Pressure sensitive liners act as another line of defense for a container’s products. They give customers confidence that their products will be kept safe and fresh. Unlike other liners, they can be applied by hand, eliminating the need for sealing equipment. This makes pressure sensitive liners cost and energy-efficient.

Pressure sensitive liners work best with bottles, jars, and canisters that store dry products. This includes powdered substances such as herbs, spices, and grated cheeses. They can also be used when storing various dry medicines and pharmaceuticals. Occasionally, they can work with thick liquids, such as creams and sauces. 

A heat induction liner (HIS) is a cap liner that sticks to the rim of a container when its seal is activated by heat. They consist of several layers, including a heat seal, a foil middle, and a backing layer. When the seal is activated, it effectively prevents leaks and contains odors. Unlike pressure sensitive liners, they are suited to hold liquids in addition to dry products. Induction liners are often used when an airtight seal is necessary. To secure them correctly to a bottle or container, a heat induction machine is required.

Induction liners typically consist of a backing layer, a foil layer, and a heat seal. For a one-piece liner, these layers are all combined into one, meaning there is a singular piece that adheres to the container. Two-piece induction liners have an added wax layer which melts during the induction process. This causes the backing layer to separate from the rest of the liner. At the end of the heat induction process, the liner is in two pieces. The backing layer will remain in the cap, while the foil layer is sealed to the container. 

Both one and two-piece liners provide airtight seals, protect from leakage, and lengthen shelf life. However, these two types of induction liners have different applications. One-piece liners cater more to single-use products, including sauces, beverages, and other goods that require protection until the moment of use. They are also used for dry products that don’t require much protection once the container has been opened. On the other hand, two-piece liners should be used if a product needs to be resealed after its initial opening. Pharmaceuticals are an excellent example, since prescriptions, pills, and other drugs must be preserved over a period of time.

To be properly sealed, induction liners require a heat induction machine. The first step is to screw the cap and liner onto the container. Then, the container's sealing head should be placed onto the induction machine. It is important to never apply the machine directly to the liner; the cap or closure must be secured to the bottle as well. When the machine is turned on, it introduces an electromagnetic current to the cap liner's conductive aluminum layer. This causes the foil's temperature to increase. As this layer heats up, the heat seal melts, bonding the foil to the container’s opening. The container is then removed from the machine, with the seal securely in place. 

The purpose of an induction liner is to create a powerful seal with the container it is attached to. If you want to create an airtight, leak-free seal, make sure to consider the material of your container. It’s important that the bottle and cap’s materials are compatible in order for the induction liner to seal properly. The container must also be able to undergo the heat induction process. If it can’t, the liner may be unable to seal itself to the container.

When selecting a heat induction liner, you should consider the amount of protection you want from the backing. Since almost all liners come with a backing layer, you should consider if you want a one-piece or two-piece liner. This will determine whether you want the backing to separate from the rest of the liner. Your product's physical qualities are a deciding factor, since some goods will affect a liner differently than others. For example, bottles that store chemicals and pharmaceuticals will require the extra protection of a two-piece liner, while foods and dry products will work with any liner.

Cap liners create powerful seals, so it is essential that the removal process is simple. If the liner is difficult to remove, it creates a negative experience for the consumer. To accommodate this, many induction liners feature clean-peel tabs for easy access. These liners feature squared-off tabs that consumers pull to remove the cover. Lift ‘n’ Peel™ induction liners are a common choice for sealing various liquids, sauces, chemicals, and more. Once removed, these products are not reusable.

Pressure sensitive and heat induction liners can only be used once. The purpose of a cap liner is to create a protective seal between the closure and the bottle. As soon as a liner is removed from the bottle or punctured, the seal is broken. The pieces that are peeled off should be properly discarded. Single-use liners are common when a bottle’s contents are used immediately after opening.

Despite having many defensive features, not all liners are tamper evident. According to the FDA, a tamper evident container must include at least one visible feature that can show users that tampering has occurred.

Pressure sensitive liners can be removed and reapplied without any visible signs, so they are not tamper evident. Heat induction liners that leave visible residue (such as bits of foil) along the container’s mouth are considered tamper evident. However, product lines such as our “Clean Peel” induction liners are not, since they can be removed in one piece.

We understand how important it is to seal products for protection and leak purposes. The Cary Company offers a wide selection of cap liners, including foam, pressure sensitive, heat induction, and sealing disc options. 

Interested in finding a specific solution? Contact one of our product specialists to answer any questions and recommend products for you. Give us a call at 630-629-6600 or email us at sales@thecarycompany.com.