Lidding Seal Temperature & Sealant Selection: PP, PE and Heat-Seal Coatings
The seal layer on a lidding film has to match the polymer actually exposed on the container rim — not the name printed on the cup. For a PP cup you typically need a PP-compatible sealant and a jaw temperature around 150–190 °C; for a PE-flange cup, a PE-compatible sealant around 120–160 °C; for a PET cup, a PET-compatible sealant around 140–180 °C. Those are screening ranges drawn from supplier data sheets, not fixed production settings — your machine, pressure and dwell time close the real window. Get the sealant right and the lid seals cleanly and peels on cue; get it wrong and you get weak seals or lids that weld shut. This page explains how to choose, with the numbers buyers actually use.
How a lidding seal actually forms
A lidding film is rarely one layer. A typical converted lid stacks an outer PET or BOPET carrier (stiffness, print surface, abrasion resistance), an optional barrier layer (EVOH, metallized PET or aluminum oxide), adhesive tie layers, and an innermost heat-seal layer that touches the container. On the sealing head, heat and pressure soften that inner sealant so it flows into the microscopic texture of the rim and re-solidifies into a hermetic bond. Only the innermost layer does the bonding — which is why the chemistry of that layer, not the outer print, decides whether the lid holds and how it opens. The logic is the same for every format: die-cut singles and rollstock share the same sealing principle.
The rule that decides everything: match the sealant to the flange, not the tray name
Here is the mistake that burns a week of line trials: specifying "a PET lidding film" for "a PET tray." A PET/PE tray often presents PE at the flange, not PET, and needs a PE-compatible sealant — not the PET-compatible one. An APET cup presents PET; a CPET tray may present a PET or CPET seal skin. Two cups both called "PP" can carry different surface formulations and seal differently with the same film. So before you choose anything, confirm three things from the container maker: the full structure, which polymer is exposed on the sealing flange, and whether that flange has a coating, seal skin or recycled-content blend. The lidding film's job is to bond to that exposed surface.
Sealant families: PE, PP, and the heat-seal coatings in between
The innermost sealant is usually a polyolefin or a proprietary coating. The common families buyers meet:
| Sealant family | Typical seal-temp window* | What it fits | Notes |
|---|---|---|---|
| LDPE / LLDPE (PE-based) | ~100–160 °C | PE-flange cups, chilled/frozen, MAP | Wide window, tolerant of contamination, low cost |
| mPE / metallocene PE | ~150–190 °C | High-speed lines, powder/fat contamination | Low seal-initiation temp, strong hot-tack |
| CPP / PP-based | SIT ~110–170 °C; seal ~150–190 °C | PP cups, hot-fill, microwave, retort-grade | Thermal stability, narrower window, tighter control |
| Ionomer | ~90–150 °C | Fatty foods, medical, contamination-prone | Premium cost, excellent low-temp seal |
| EVA | ~130–160 °C | EPS / PS cups | Low-temp tack, common on PS |
| Universal / proprietary coating | Often ~100–220 °C | PP / PE / PET / PS | Convenience vs cost and recyclability |
*Screening ranges from supplier technical data and published references, not guaranteed production set points. Always close the window on your actual machine.
Sealing temperature by container material
| Container (flange) | Typical jaw trial range* | Compatible sealant | Peel method | Typical use |
|---|---|---|---|---|
| PET / APET | 140–180 °C | PET-compatible copolyester | Interfacial / controlled | Deli, salad, ready meal |
| PET/PE (PE exposed) | 120–160 °C | PE-compatible | PE easy / cohesive | Chilled, frozen, MAP |
| PP | 150–190 °C | PP-compatible | PP easy / lock | Dairy, sauce, microwave, hot-fill |
| PS | 120–160 °C | EVA / modified PO | Adhesive | Yogurt, deli |
| CPET | 175–210 °C | CPET/PET-compatible coating | Cold easy / heat-release | Dual-ovenable meals |
Note the spread inside one family: PP spans roughly 150–190 °C depending on whether it is mono-PP, a copolymer, or a retort grade. CPET needs oven-qualified components through the whole pack — film, coating, adhesive, ink — not just the lidding film.
Peel strength: easy, medium, strong
Peel force is what the consumer feels and what the supply chain needs. Published references put easy-peel lids in a rough 5–15 N/15 mm window — lower (about 5–8 N) for consumer-friendly yogurt lids, higher (10–15 N) where tamper evidence matters, such as medical packs. Two failure modes matter:
Cohesive peel — the sealant splits within itself; common on PE-to-PE and PP-to-PP easy-peel. Clean, consistent, low residue.
Adhesive / interfacial peel — the bond lets go at the film–flange interface; common on PET (ionomer / EAA) and PS (EVA) systems.
A practical caveat from packaging testing: peel force tends to rise at refrigeration and freezing temperatures because the failure mode shifts. Validate at the temperature your product actually ships and stores, not just at room temperature. ASTM F88 is the standard method used to measure seal strength on flexible barrier materials.
Why temperature alone is not the setting
Seal temperature is one of three coupled parameters. Too low and the sealant never fully melts — a cold, weak bond. Too high and you risk burn-through, shrinkage of oriented film, sealant squeeze-out, or a lid welded shut. Pressure drives contact and pushes air out; dwell time lets heat transfer through the laminate. Contamination on the flange — oil, sauce, powder — is the most common real-world leak source, and no sealant choice fixes a dirty rim. So the right answer is never "set it to 180 °C"; it is "run a temperature ramp on our cup, with our filler, at our line speed, and lock the window where seals pass at ambient and at cold-chain temperature." Your lidding supplier should hand you a starting window from their data sheet; you confirm it on the machine.
How to choose the sealant for your product
What is the cup made of, and what is on the flange? Match the sealant to the exposed polymer first.
What is the fill temperature and life cycle? Cold-fill chilled dairy → PE or PP easy-peel. Hot-fill or microwave → PP-based. Retort (121 °C+) → a dedicated retort-grade sealant and film.
How should it open? Easy peel for consumers; lock seal (cut or tear) for maximum security; heat-release for ovenable meals.
Do you need barrier? The sealant does not supply oxygen barrier — that is the foil or EVOH / AlOx layer above it. Pick barrier by product, sealant by cup.
Metal detection or recyclability? Foil masks metal detectors; a mono-PET or mono-PP lid with a matching cup is the cleaner recyclable route. Universal coatings trade some of that away for convenience.
When a different route is better
Retort products. Standard easy-peel sealants for ambient or chilled use fail at sterilization temperatures. Use a retort-qualified grade and validate the whole pack.
Strict mono-material recyclability. A foil–plastic laminate is mixed and harder to recycle. Choose mono-PP or mono-PE lid plus cup.
Heat-sensitive or very low-temperature filling. Reach for low-SIT sealants (ionomer, mPE) so you seal at a lower jaw temperature and protect the product.
Unknown flange. If you cannot confirm the exposed polymer, stop and get the container spec. Guessing costs more line time than asking.
What to send your lidding supplier for a quote
To get a usable quote instead of a price guess, hand the converter the real variables:
Container material and the exposed flange polymer (PP / PE / PET / PS / glass).
Cup diameter and shape (round / square / rectangular; pull tab yes or no).
Product and fill temperature (cold / hot-fill / retort).
Required peel (easy / medium / strong) and any lock-seal need.
Barrier requirement (foil, metallized PET, EVOH, or none).
Print (colors, artwork format, embossing pattern).
Quantity per design and annual volume.
Destination market and any food-contact certification needed.
FAQ
What sealing temperature do lidding films need?
There is no single number. Typical jaw trial ranges from supplier data are about 140–180 °C for PET cups, 150–190 °C for PP cups, 120–160 °C for PS cups, and 175–210 °C for CPET trays. Those are screening ranges — your machine, pressure and dwell time set the real window, so confirm it on your line.
What is the difference between a PP sealant and a PE sealant for lidding?
Both are polyolefin seal layers, but a PP-compatible sealant bonds to PP flanges and tolerates higher heat (hot-fill, microwave, retort grades), while a PE-compatible sealant bonds to PE-exposed flanges and seals at a lower temperature with a wider, more contamination-tolerant window. The cup's exposed rim — not the cup's name — decides which one you need.
Why won't my lidding peel, or why is the seal weak?
Common causes: wrong sealant for the flange polymer, jaw temperature too low (cold, weak bond) or too high (welded shut / burn-through), contamination (oil, sauce, powder) on the rim, or inconsistent web tension on a high-speed line. Validate the seal at the temperature your product is stored, not just at room temperature.
What is the difference between easy peel and lock seal?
Easy peel opens with a controlled, clean force (roughly 5–15 N/15 mm, lower for consumer lids) so the user peels it back. Lock seal forms a permanent closure opened by cutting or tearing, used where maximum security is needed. Heat-release peel is for ovenable meals that vent as they heat.
What food-contact rules apply to lidding film?
In the U.S., food-contact materials fall under FDA 21 CFR; in the EU, under Framework Regulation (EC) No 1935/2004. Gerun Packaging holds ISO 9001 and uses food-contact testing validated by an FDA-accredited laboratory. Confirm the specific compliance for your destination market when you inquire.
What is the minimum order and lead time for custom lidding?
At Gerun Packaging, custom lidding starts at 10,000 pieces per design, with lead time typically 15–25 days after artwork approval. Industry minimums vary by supplier, so confirm per quote.
Conclusion
The seal layer is the part of a lidding film that decides whether your pack holds and how it opens, and it has to match the polymer on the cup rim — PP cups to PP-compatible sealants around 150–190 °C, PE-flange cups to PE-compatible around 120–160 °C, PET cups to PET-compatible around 140–180 °C. Those are starting windows from supplier data, not set points; close them on your machine at ambient and cold-chain temperature. Gerun Packaging is an OEM/ODM flexible-packaging manufacturer supplying aluminum-foil and plastic lidding film; our die-cut lidding guide covers format choice and our lidding film overview lists materials and structures. When you are ready to spec a run, send us your cup material, diameter and fill temperature — we will recommend the sealant and confirm the seal window. For the material call between foil and metallized PET, see our foil vs metallized PET comparison; for converted rollstock, our rollstock lidding guide; and for end-use examples, our lidding applications guide.
