You can run polyester film on the same metallizer you use for BOPP — but you cannot run it on the same recipe. Metallizing PET film demands four changes: a moisture plan, a lower tension setpoint, a re-checked dyne level, and a grade-specific drum temperature. Skip those changes, and you get pinholes, curl and adhesion failures that operators usually blame on the machine.

Polyester behaves differently from BOPP for measurable reasons. It carries water inside its polymer structure, it runs stiffer under tension, and it reaches adhesion-ready surface energy through different chemistry. Once you align the recipe with those properties, PET rewards you with the smoothest, highest-gloss aluminium layer of any common substrate.

What Makes Polyester Different From BOPP Inside a Vacuum Chamber?

Both films are biaxially oriented and both accept evaporated aluminium. However, they differ in four properties that directly drive recipe settings: water uptake, elastic modulus, surface chemistry and thermal behaviour. Each one changes what you set on the control panel.

Difference 1 — Polyester Holds Water, BOPP Does Not

Polyester absorbs water molecules into its amorphous regions, and that absorbed water plasticises the polymer (ScienceDirect study on PET water absorption). BOPP, by contrast, is a non-polar hydrocarbon that takes on almost no moisture.

That difference shows up the moment you pump down. Water leaves the PET web, raises the chamber pressure, and competes with aluminium vapour for the same space. Operators then see four symptoms:

• Pinholes and haze in the aluminium layer
• An evaporation rate that drifts mid-run
• A longer pump-down than the BOPP recipe expects
• Optical density that varies from the start of the roll to the end

What to change: condition and dry the roll before loading, keep the film store at a controlled humidity, keep rolls wrapped until the last moment, and re-check the roll if it sat in a humid warehouse. Our own line experience with this failure mode is documented in substrate outgassing and moisture control.

Difference 2 — Tension Setpoints Do Not Transfer

Polyester carries a tensile modulus around 3.87 GPa (PET film property data), which puts it well above the softer polyolefin films. Feed the same N/m tension into a PET web and you load far more stress into the material. In practice, PET tells you it objects through curled edges, wrinkled shoulders, telescoped rolls and fine surface scratches that later read as coating defects.

What to change: rebuild the tension setpoint from the PET datasheet instead of copying the BOPP value, use taper tension through the wound roll, and watch the web at the unwind rather than at the rewind. Two of our technical notes cover the mechanics: web tension control in roll-to-roll metallizing and wrinkles and curl in metallized film.

Difference 3 — Surface Energy and Pre-Treatment Work Differently

This is where polyester actually helps you. Untreated, uncoated PET generally shows a surface energy around 43 dyn/cm (Accu Dyne Test technical Q&A), while polyolefins such as BOPP start far lower and need aggressive treatment before any ink or adhesive will hold. PET already presents polar ester groups at the surface, so you need a lighter treatment to reach the same adhesion result. Industry references publish target ranges per polymer and per ink system (Enercon surface-energy and treatment range reference).

However, “easier” does not mean “safe to ignore”. PET’s advantage decays: stored rolls lose treatment over time, and low-molecular-weight oligomers migrate to the surface and weaken bonding. Therefore, verify the dyne level with test pens at every roll change rather than trusting the label on the box.

What to change: check dyne level on the incoming roll, re-check it after storage, and confirm the result with a tape or cross-hatch pull test. We cover both steps in corona treatment and surface energy and metallized film adhesion testing.

Difference 4 — The Thermal Window on the Drum Differs

Polyester’s glass transition temperature sits near 78 °C (PET film substrate technical resource). Above that point the oriented structure starts to relax, so drum temperature and dwell time decide whether you get a dimensionally stable web or a shrunken, curled one.

BOPP softens through a different mechanism, which means a drum setpoint that works for one film does not transfer to the other. Heat-stabilised (heat-set) PET grades tolerate a wider window, and they are the right choice when you need a warmer drum to hit a specific aluminium thickness.

What to change: set the drum temperature per PET grade, write it into the recipe, and log the actual drum temperature per batch. Our analysis of chill roll temperature in vacuum metallizing explains what the drum controls in the deposition zone.

The PET vs BOPP Metallizing Recipe: Side by Side

Treat this table as a starting point, not a substitute for a trial roll. Every PET grade carries its own slip package, primer and heat history.

How to Set Up a PET Recipe on a Machine That Already Runs BOPP

Follow these eight steps in order. They turn a BOPP recipe into a repeatable PET recipe in one shift.

1. Confirm the PET grade. Ask whether the film is heat-stabilised, whether it carries a primer, and whether the supplier already treated it.
2. Condition the roll. Give the film time in a controlled-humidity area before it reaches the machine.
3. Establish base pressure with the web loaded. Load a full roll, then find your real working pressure rather than the empty-chamber figure.
4. Rebuild tension from the PET datasheet. Start lower than the BOPP value and raise it until the web tracks flat.
5. Set drum temperature for the grade. Record the number that produced a flat, curl-free web.
6. Verify the dyne level, then run an adhesion pull test. Confirm both before you commit the roll.
7. Run an optical density coupon. Check uniformity across the web width and log the values.
8. Lock and version the recipe. Keep the setpoints with the batch record so the next run starts from data, not memory.

For a refresher on what happens inside the chamber during these steps, see how a vacuum coating machine works, plus our notes on optical density and aluminium layer thickness and barrier performance.

Which Machine Configurations Suit Polyester Film?

A suspension-type roll-to-roll metallizer handles PET and BOPP on the same platform, because the chamber, pumping set and winding system stay the same while the recipe changes. Three machine features decide how easily you switch between the two films:

• Automatic tension control, which holds PET stable at lower setpoints
• Grade-specific drum temperature control, including cooling capacity for thin gauges
• Recipe management, so the operator loads a saved PET recipe instead of re-tuning

When you need aluminium layers above 800 Å for medical or high-barrier packaging, an induction-heated machine with graphite crucible evaporation sources gives you the deposition rate that thick layers require. Tempo Machinery builds these configurations on one platform — see the fully automatic suspension vacuum coating machine and the induction heating vacuum metallized machine, and the metallized PET film range that runs on them.

Quality Checks That Catch PET-Specific Problems

Run these five checks on every PET batch, because each one catches a failure mode that BOPP operators rarely meet:

1. Pinhole count — the first indicator of a moisture problem
2. Adhesion — tape test or cross-hatch pull test, at the roll start and roll end
3. Curl and flatness — sample a strip after coating and let it relax
4. Optical density uniformity — measure across the web width, not only at the centre
5. Barrier verification — confirm water vapour transmission rate against ISO 15106-2 (ISO 15106-2 standard) when a customer specifies a barrier target

Where Compliance Enters the Recipe

A metallized PET structure usually ends up in food, pharmaceutical or consumer packaging, so the compliance question sits with the finished laminate rather than with the coating step alone. Two European frameworks matter here: plastic food contact materials fall under Regulation (EU) No 10/2011, and packaging placed on the EU market now follows the recyclability and design requirements of Regulation (EU) 2025/40 (PPWR). Confirm the requirements with your converter and your compliance lab before you commit a specification.

Frequently Asked Questions

1. Can I metallize PET film on a machine set up for BOPP? Yes. Change four things first: the moisture plan, the tension setpoint, the drum temperature and the pre-treatment check. The hardware stays the same.

2. Why does PET need drying when BOPP does not? Polyester absorbs water into its amorphous regions, so the web releases moisture in vacuum and disturbs the deposition process. BOPP absorbs almost nothing, which keeps its outgassing load low.

3. Does metallizing PET film require corona treatment? Untreated PET already measures around 43 dyn/cm, so it starts higher than polyolefins. Nevertheless, you should verify the dyne level on each incoming roll, because treatment decays during storage.

4. What causes pinholes in metallized polyester film? Moisture drives most of them. Water vapour from the web lifts the chamber pressure, the aluminium vapour scatters, and thin spots become pinholes. Check roll conditioning before you touch the evaporation source.

5. Why does my metallized PET curl when BOPP runs flat? Two causes dominate: too much tension for a higher-modulus film, and a drum temperature that relaxes the oriented structure. Lower the tension and set the drum per PET grade.

6. What aluminium thickness should I target on PET? Most packaging work lands between 300 Å and 600 Å, while medical and high-barrier applications push past 800 Å. Match the thickness to the barrier specification and verify it with optical density readings.

7. Can one metallizer run PET, BOPP, CPP and PE? Yes, and most converters do exactly that. Automatic tension control and saved recipes make the switch practical; substrate-specific settings make it reliable.

8. How do I know whether moisture is the real problem? Watch the pump-down curve and the pinhole count together. A slower pump-down with a rising pinhole count points to the web, not to the pumps.

Metallizing PET film works best when you treat polyester as its own process, not as a BOPP variant. Build a moisture plan, rebuild the tension setpoint, verify the dyne level, and set the drum temperature for the grade — then log everything so the next roll repeats the result. Polyester will pay you back with a smoother aluminium layer and a tighter uniformity window than any other common substrate.

Need a machine that runs PET, BOPP and CPP from saved recipes? Send us your film specification and our engineers will map the recipe to your target barrier and thickness.