You’ve picked out the perfect container. The liner inside the cap is what keeps your product from leaking, protects its shelf life and can show customers that it hasn’t been opened. This guide explains how each type of liner seals and which one is right for your product.
Not sure which you need? Reach out by email, chat or phone. We’re happy to help, and we can send free samples so you can test before you buy.
Unlined caps
An unlined cap has no liner, so the seal depends only on how the cap and container fit together. Standard unlined caps are best for dry products, because liquids are likely to leak.
Some caps are made “linerless”, with a sealing ring or plug molded into the cap itself. Those are designed to seal without a liner, so check the product details for your cap.
Best for
- Dry goods and cosmetics
- Products where leak protection and tamper evidence aren’t a priority
Watch out for
- Liquids, unless the cap has a built-in seal
Foam liner
Foam liners are a general-purpose, economical liner made of low-density polyethylene (PE) foam. The foam compresses against the container rim when the cap is screwed on tightly, and it stays in the cap so it reseals every time.
F217 is a common type of foam liner: a foam core between two thin polyethylene layers, which gives a smooth sealing face.
Best for
- Foods and beverages
- Cosmetics and personal care
- Industrial and household chemicals
Good to know
- Reusable: it stays in the cap for repeated opening and closing
- It doesn’t provide tamper evidence on its own
Cone liner
A cone liner is a cone-shaped polyethylene liner. When the cap is tightened, the cone presses into the container opening and seals against the inside edge, as well as the top of the rim. It stays in the cap and reseals each time.
Best for
- Liquids and oils
- Products in narrow-neck bottles
Good to know
- Reusable, with no tamper evidence on its own
Pressure sensitive liner
Pressure sensitive liners are designed to seal dry products. They’re activated by torque: screwing the cap on tightly presses the liner’s adhesive onto the container rim. When the customer opens the cap, the seal stays on the container and is peeled off.
Best for
- Powders
- Tablets, capsules and other pharmaceuticals
- Dry supplements
Tips for a good seal
- Make sure the container rim (landing) is clean and free of powder before capping
- Screw the cap on tightly; the seal needs pressure to bond
- Let the seal sit for 24–48 hours to fully adhere
Watch out for
- Liquids and oily products; this liner is made for dry products
Pressure sensitive + foam liner
This liner combines the two: a pressure sensitive seal sits on top of a foam liner. The seal bonds to the container rim, and once the customer peels it off, the foam liner stays in the cap to reseal the container between uses.
Best for
- Powders, tablets and capsules that need resealing after the first opening
The same tips apply as for pressure sensitive liners: keep the rim clean, tighten the cap firmly and allow 24–48 hours to fully adhere.
Heat seal (induction) liner
A heat seal, or induction, liner creates an airtight, single-use seal. The liner has a thin layer of foil. After capping, the container passes under an induction sealing machine, which heats the foil and bonds the liner’s sealing layer to the container rim. You need an induction sealer to activate these liners.
Heat seal liners are made to bond with a specific container material:
- For PET: PET containers
- For PE: polyethylene containers, such as HDPE
- Universal: bonds to most container materials
Check that the liner matches your container, because a liner made for the wrong material won’t bond properly.
Best for
- Liquids
- Food
- Pharmaceuticals and supplements
Good to know
- The airtight seal helps prevent leaks and protects freshness
- Tamper-evident: customers can see if the seal has been broken
Choosing the right liner
- Dry goods, no seal needed: unlined
- Everyday liquids, foods and cosmetics with a reusable seal: foam or F217
- Liquids and oils in narrow-neck bottles: cone
- Powders, tablets and capsules: pressure sensitive, or pressure sensitive + foam to reseal after opening
- An airtight, tamper-evident seal for liquids, food or pharmaceuticals: heat seal (requires an induction sealer)
Disclaimer: This information is based on general industry recommendations and is not a guarantee. It is the customer’s responsibility to test for product compatibility; we’re happy to send free samples so you can test before you buy.
