A cup may look simple, but the surface a lid seals to is often more specific than its product name suggests. A “paper cup” may have a PE or PP coating at the rim. A PET cup may have a treated or coated flange. A film that seals well on one cup can fail on another cup with a similar appearance.
For this reason, the first question is not “What temperature should we use?” It is: what is the actual sealing interface?
Start with the cup-rim material
The seal layer must be designed for the material that touches the lid. Common interfaces include PP, PE-based surfaces, PS, selected PET structures, coated paperboard and coated metal containers. The outer cup body does not always identify the sealing surface.
Ask the cup supplier for the resin family, coating information and any surface treatment. If that information is unavailable, send physical samples for evaluation. A short trial with the real cup is more useful than choosing a film by name alone.
PP cups
PP is widely used for dairy, snacks, instant meals and hot-fill applications. It can offer useful heat resistance, but its sealing result still depends on cup-wall thickness, flange flatness, machine dwell time and the chosen sealant formulation.
For PP cups, define whether the required opening is peelable or permanent. A peelable lid needs a controlled opening force. A permanent seal needs different performance targets and is often opened through another feature.
PET cups
PET is common where clarity and presentation matter. However, untreated PET is not automatically compatible with every heat-seal film. The seal layer must be developed for the actual PET surface or coating, then tested under the intended production conditions.
When briefing a supplier, include filling temperature, storage conditions, product acidity or fat content, and whether the cup is subject to later heating or cooling.
PS cups
PS is frequently used in dairy and portion-pack formats. Its heat sensitivity makes a wide process window important. Excessive sealing energy can distort a thin flange; too little energy can create weak areas or channels.
Rather than requesting one “recommended temperature,” run a small test matrix across realistic temperature, pressure and dwell-time settings. Record the failure mode as well as the peel or seal-force result.
Paper cups are usually coated cups
The important question for a paper cup is not only the paper grade. It is the sealing layer at the rim. That surface may be PE, PP or another coating. The same paperboard body can therefore require different lid-film structures.
Check the cup rim for seams, wrinkles and coating consistency. A sound film cannot compensate for a damaged or uneven flange.
Five details to provide before sampling
- Cup sample or a dimensioned drawing, including rim diameter and flange width.
- Actual sealing-surface material or coating information.
- Packed product and filling conditions.
- Sealing-machine type, line speed and available temperature, pressure and dwell-time range.
- Required opening behavior: peelable, permanent or another controlled opening method.
Evaluate the complete package, not only the first seal
A good sample should be checked beyond its first appearance. Confirm seal consistency around the rim, opening behavior, hot performance where relevant, leak resistance and the effect of transport or storage.
For a fuller explanation of the process, read What Is Heat Sealing Film and How Does It Work?. If your project also requires a pre-cut lid, compare aluminum foil and foil-free food lids.
Need a cup-specific recommendation?
HYPack develops custom heat-sealing film and food-lid structures. Send the real cup, substrate details and line conditions so the film can be assessed against the interface it must seal.
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