Both systems close a flexible pack. Only one of them puts heat into your product. That single difference decides most of what follows: which films you can run, how fast the line goes, what the seal costs you, and whether the pack survives the recycling stream it ends up in.
The two systems, stated plainly
Heat seal works by melting. A lacquer is coated onto the web, and when the jaws close they push thermal energy through the substrate until the coating softens and flows. The layers fuse, the jaws open, and the seam sets as it cools. The bond is made by the coating and the material becoming, briefly, one thing.
Cold seal works by cohesion. A water-based latex is coated onto the web, and it bonds only to itself. Bring two coated faces together under nip pressure and they join instantly. No heat enters the process at any point. The product inside never knows a seal was made.
That is the whole distinction, and every practical consequence below follows from it.
1. Is the product heat-sensitive?
This is the first question, and for a large share of lines it is the only one that matters. Chocolate blooms. Ice cream melts. Some pharmaceutical actives degrade. Fresh bakery goes soft. If the product cannot tolerate a hot jaw sitting against it for a dwell period, heat seal is out regardless of every other advantage, and cold seal is not a preference but a requirement.
If the product is thermally indifferent, the question stays open and the remaining factors decide.
2. How fast is the line, and what kind is it?
Cold seal is materially faster on flow-wrap. There is no heat-up, no dwell period waiting for a coating to reach its melt point, and no cool-down before the seam can take load. The nip closes and the seal exists. On high-speed horizontal flow wrap, this is often worth more than the coating cost difference.
Heat seal needs dwell time. That dwell is a real constraint on throughput, and it is the reason a converter chasing line speed on a heat-sealed structure ends up pushing jaw temperature upward, which brings its own problems.
3. What is the sealing window on your substrate?
A sealing specification that quotes one number is quoting the easy one. Three properties define the window, and none can be inferred from the others.
- Seal initiation temperature. The lowest jaw temperature at which the coating flows enough to form a seal. It sets the floor of the operating window.
- Hot tack. The strength of the seal measured while the sealant is still molten, under ASTM F1921. On a form-fill-seal line the pack is loaded before the seam has cooled: product drops onto the bottom seal, film tension pulls on the vertical seal, the conveyor handles the pouch. Hot tack is what holds during that moment.
- Seal strength. The peel strength of the finished, cooled seam, under ASTM F88, reported as force per unit width. This is the number most datasheets lead with.
The trap is assuming the third predicts the second. It does not. A film can produce excellent cooled seal strength and still split open on the line, because by the time a laboratory specimen has been conditioned and pulled, the hot tack failure mode has disappeared. A cooled seal test cannot detect it.
If your initiation temperature is high, the instinct is to run the jaws hotter. That slows the line, distorts the film and starts scorching the print. The correct fix is a coating formulated to seal lower, not a hotter machine.
4. What does each system cost you in practice
Cold seal latex is generally the more expensive material per kilogram, and it carries two additional requirements that heat seal does not. It needs a release lacquer on the reverse face wherever the substrate is untreated, or the reel blocks to itself. And it is more sensitive in storage and transit, because the property that makes it work at ambient temperature is the same property that makes it bond when you did not intend it to.
Heat seal lacquer is usually cheaper per kilogram, and the cost moves to the line instead: energy into the jaws, dwell time out of your throughput, and a narrower tolerance for film variation.
Comparing the two on price per kilogram alone will mislead you. Compare cost per thousand packs, with line speed included.
5. Where the recycling requirement now sits
Regulation (EU) 2025/40, the Packaging and Packaging Waste Regulation, entered into force on 11 February 2025 and has applied generally since 12 August 2026. It requires all packaging placed on the EU market to be recyclable, in an economically viable way, by 2030, and it restricts substances of concern including PFAS in food-contact packaging above defined thresholds.
For flexible packaging this lands as a materials problem. The multi-material laminate that seals beautifully (printed PET, foil barrier, PE sealant) is precisely the structure recycling streams reject. The direction of travel is mono-material: an all-PE or all-PP pack a single stream can process.
Mono-material changes the sealing question in a specific way. In a conventional laminate you have a low-melt PE layer sitting beneath a high-melt PET one, and that temperature gap is what gives you a comfortable window. Remove it and the layer you are trying to seal and the layer you must not melt are the same polymer. The window narrows sharply. Sealing then depends on a coating with a genuinely low initiation temperature, applied thinly enough that it does not compromise the recycling stream it was chosen to protect.
Cold seal has an advantage worth noting here: because it introduces no heat, it does not care about the melt behaviour of the substrate at all. On a mono-material structure that is not a small point.
6. Food contact: what the frameworks actually require
Both systems are regulated, and they are regulated under different sections.
- Regulation (EC) No 1935/2004 is the European framework for all food-contact materials. Regulation (EU) No 10/2011 governs plastics, setting the Union list of authorised substances, specific migration limits and an overall migration limit. A layer not in direct food contact may use non-listed substances provided they are not mutagenic, carcinogenic, toxic to reproduction or in nanoform: this is the functional-barrier logic most laminate structures rely on.
- Regulation (EU) 2025/351 has applied since 16 March 2025 and tightens the handling of non-intentionally added substances and of what the Declaration of Compliance must carry. The transitional period for material placed on the market under the previous rules closes on 16 September 2026.
- In the United States, 21 CFR 175.105 covers adhesives and 21 CFR 175.125 covers pressure-sensitive adhesives, which is the section that governs cold seal. Coatings sit under 21 CFR 175.300 and, for polyolefin films, 175.320.
Ask any supplier for the technical data sheet and safety data sheet that match your structure, not the product family. A family sheet cannot answer a migration question.
7. How to run a trial that actually tells you something
A sample that has not met your line is not a recommendation. Before requesting one, have four things written down:
- Substrate and full structure, layer by layer, including treatment level and whether any face is untreated.
- Line type and speed: VFFS, HFFS or flow wrap, and the actual running speed, not the machine’s rating.
- Jaw temperature and dwell you currently run, and what you are willing to change.
- Fill weight and seal geometry, because these set the hot tack requirement.
With those four, a formulator can propose a grade with reasoning behind it. Without them, any recommendation is a guess dressed up as a specification.
Summary
Choose cold seal when the product cannot take heat, when flow-wrap line speed is the binding constraint, or when a mono-material structure has closed your thermal window. Accept in exchange a higher material cost, a release lacquer requirement on untreated faces, and more careful storage.
Choose heat seal when the product is thermally robust, when you are sealing to a rigid container or lidding foil, and when dwell time is available in your cycle. Accept in exchange the energy cost and a tighter dependence on consistent film behaviour.
In both cases, specify the coating by its sealing window rather than its price, and validate it on your own line before it goes into production.
Frequently asked questions
Can cold seal adhesive be used on any film?
No. Cold seal bonds only to itself, so both faces that meet must be coated. On untreated substrates a release lacquer is also required on the reverse face, or the reel blocks to itself in storage. Corona-treated OPP, metallised films and plain PP are the usual starting points.
Why does a seal pass the laboratory test but fail on the production line?
Because the laboratory usually measures cooled seal strength under ASTM F88, while the line loads the pack while the seam is still molten. The property that governs that moment is hot tack, measured under ASTM F1921. A cooled seal test cannot detect a hot tack failure, since the failure mode has disappeared by the time the specimen is conditioned and pulled.
What is seal initiation temperature and why does it matter?
It is the lowest jaw temperature at which the coating flows enough to form a seal, and it sets the floor of your operating window. A high initiation temperature forces you to run the jaws hotter, which slows the line, distorts the film and can scorch the print. On mono-material structures a low initiation temperature is often the deciding property.
Does PPWR mean we have to change our sealing chemistry?
Not directly. Regulation (EU) 2025/40 requires packaging on the EU market to be recyclable in an economically viable way by 2030, which pushes converters toward mono-material structures. It is that structural change, not the regulation itself, that narrows the sealing window and changes what the coating has to do.
Which regulations apply to heat seal and cold seal in food contact?
In the EU, Regulation (EC) 1935/2004 is the framework and Regulation (EU) 10/2011 governs plastics, as amended by (EU) 2025/351 whose transitional period closes on 16 September 2026. In the United States, 21 CFR 175.105 covers adhesives, 21 CFR 175.125 covers pressure-sensitive adhesives including cold seal, and 21 CFR 175.300 and 175.320 cover coatings.