Pre-printed sleeves (usually comprised of PVC, PETG or OPS film) are placed over the container, and then sent through a heat tunnel. The application of the heat shrinks the film until it tightly conforms to the shape of the container.
Advantages of shrink sleeve labeling:
Conforms to containers of any shape
Provides tamper-evident protection when covering lids and closures
Protects container from scratches
Can accommodate low-minimum runs