Common Packaging Formats: Seals

Emily Hawley

Updated 23 July 2025 12:52

Bottle Seals

Some cap applications, require an internal seal / membrane which can be made of several materials including aluminium foil / paper, PVC foam, plastic and paper.

If the seal remains on the bottle/jar/container and must be removed by consumer to reach contents, it must be counted as a separate component. Some applications retain the seal/membrane in the cap at all times and it cannot be removed, therefore it needs to be included with the cap as a different material. It will become mixed material as parts are not compatible with recycling as they are not easily separated.

Below are just a couple of examples of each.

Flexible Plastic Seal Types

Bead weld Seal on two sides of bag with no overlap, suitable for lightweight constant size items as not the strongest seal
Crimp weld Seal on two side with overlap, for heavier items, frozen food bags, pouches etc. as stronger seal option than bead.
Fin Seal Back seal on VFFS or HFFS wrappers where film is overlapped to form a crimped seal on spine of pack, the seal is loose from the pack.
Lap Seal Similar to fin seal, but material is welded to back of bag, giving a neater finish.
Roll top seal Used on products where layers of seal are required for extra moisture barrier or contents are able to escape easily, generally used in packing sugar flour, etc.
Tie top seal Bread bag tie top requires tape or twist tie closure.