Synthetic paper is bought for one reason: it has no wood fibre in it. Once the fibre is gone, water stops swelling the sheet, tears stop propagating, and the material stops caring which way the grain runs. Everything else buyers argue about — whiteness, stiffness, print method, price — is a consequence of which polymer route the mill chose, and the three routes sold under the same name behave very differently on press.
Model guide · last verified 2026-10-21 · published in English · technical questions: contact the lab
A synthetic sheet is a plastic film loaded with mineral filler — usually calcium carbonate — and drawn biaxially so the filler particles leave micro-voids around them. Those voids are what make the sheet opaque and paper-white without any pigment sitting on the surface. No cellulose means no fibre, and no fibre means the sheet cannot take up water, cannot delaminate when it does, and has no grain direction to curl against.
Three commercial routes sit under the same phrase, and they are not interchangeable:
Cast mineral-filled sheet is the heaviest filler load, drawn to a matte, paper-like hand. It is the closest thing to paper in feel and the most expensive per square metre. It prints well by offset and by water-based flexo because the surface is genuinely absorbent-looking, though it is still a plastic sheet and still needs a treated or coated face.
Cavitated BOPP is ordinary BOPP with a cavitating agent that opens voids during stretching. Density drops to roughly 0.6 g/cm3 against 0.91 for solid BOPP, so at the same caliper it is lighter and softer, with the pearlescent sheen that gives the grade its trade name. It is the cheapest way to get an opaque white film facestock.
Topcoated white BOPP or PET is a solid white film with a print-receptive coating on the face. It has no void structure at all, so it is the most dimensionally stable of the three and the most consistent batch to batch — which is why it is the default for barcode and variable-data work where dot gain has to stay put run after run.
| Route | Structure | Typical use | Where it loses |
|---|---|---|---|
| Cast mineral-filled sheet | Heavily filled biaxial PP, matte | Premium retail, offset-printed tags, paper-feel labels | Highest cost; least tolerant of tight die-cut windows |
| Cavitated (pearlised) BOPP | BOPP with internal voids, density ~0.6 | Opaque white film labels, beverage and household | Softer under the blade; pearlescent sheen is not wanted on barcode areas |
| Topcoated white BOPP / PET | Solid white film plus receptive topcoat | Barcode, variable data, thermal transfer, small text | Less paper-like hand; PET costs more than BOPP |
Water and humidity. A paper label absorbs moisture through its edges and its back, swells, and then dries back unevenly — which is why paper labels on chilled or frozen packs curl at the edges after a few days in the cold chain. A fibre-free sheet has nothing to swell. The adhesive and the liner still matter, but the facestock stops being the variable.
Tear and abrasion. Paper tears along a line once a nick forms. Film does not: the polymer chains redistribute the stress, so a scored or nicked label keeps its shape. On squeezable bottles and on packs that rub against each other in a case, that difference shows up as labels that are still legible at the end of the journey.
Fibre and dust. Paper generates particulate when it is slit, die cut and matrix-stripped. In pharma, electronics and cleanroom assembly that dust is a defect source. Film produces cut edges, not fibre shed, which is one of the reasons synthetic facestocks dominate those rooms.
No grain direction. Paper has a machine direction and a cross direction, and it curls differently along each. Film is far closer to isotropic, so a label that is dimensionally stable in one orientation is stable in the other too. That matters most on small, tightly curved containers, where paper grain fights the curvature of the container.
The honest counterweight: none of this is free. Synthetic facestock typically runs well above the paper equivalent per square metre, and the gap has to be paid for by a failure the paper version would actually suffer. If the pack never sees water, never gets squeezed and never enters a cleanroom, coated paper is the better buy and we say so.
Film is sold in microns and buyers think in mils, and the two convert at 25 µm to 1 mil, so 36 µm is about 1.4 mil and 50 µm about 2 mil. That part is simple. The part that goes wrong is grammage: synthetic sheet is often quoted in gsm because it is bought alongside paper, but density varies by a third between cavitated and solid film. An 80 µm cavitated sheet weighs roughly what a 50 µm solid sheet weighs, so two quotes in "80 gsm synthetic paper" can be different materials at different calipers.
Our rule is to specify caliper in microns and let the mill confirm grammage, because caliper is what the die, the blade and the applicator actually see. Stiffness follows caliper far more closely than it follows weight, and stiffness is what decides whether the label can be dispensed at line speed without the web folding over on the peel plate.
| Caliper | Approx. | Stiffness behaviour | Usually specified for |
|---|---|---|---|
| 25–30 µm | 1.0–1.2 mil | Very conformable, needs care on high-speed dispensing | Squeezable bottles, tight curves, wrap-around |
| 36–40 µm | 1.4–1.6 mil | The balanced default; dispenses cleanly on most lines | Beverage, household, general purpose film labels |
| 50 µm | 2.0 mil | Firmer, holds a flat face, less willing to follow a curve | Large labels, flat panels, premium hand |
| 75–100 µm | 3–4 mil | Rigid enough to be handled as a card; not for tight curves | Durable goods, tags, removable and re-sealable work |
Polypropylene has a low surface energy — around 29 to 31 dyn/cm — and most inks need the substrate to sit at 36 to 38 dyn/cm before they will anchor properly. That gap is the single most common reason a synthetic label prints with patchy solids, mottled images or ink that rubs off after a week. The fix is a treatment, not a different ink: corona discharge, flame treatment, or a receptive topcoat applied at the coating stage.
Which treatment is right depends on the press. Water-based flexo and offset want a high, even dyne level and a surface that wets out; UV offset and UV flexo are less sensitive to dyne level but very sensitive to surface contamination, so a sheet that sat unpacked in a dusty plant will print badly regardless of its treatment. Thermal transfer is a separate case: wax ribbons smear on film, so film facestocks need a resin or resin-wax ribbon and a printer setting that matches the caliper.
Laser printing is where thin film gets punished. The fuser runs hot, and a 36 µm sheet with a light liner can wave, shrink or jam in the fuser path; sheet-fed laser work is safer at 80 µm and above, or on a topcoated grade sold specifically for it. Aqueous inkjet is the reverse problem — the ink needs somewhere to go, so it requires a receptive coating rather than a treatment. If you are printing aqueous inkjet, the coating decision comes before the facestock decision.
We test rather than assume: dyne pens across the web at the start and end of a run, then a real print trial on the actual press. A dyne reading that starts at 38 and falls to 32 across a 6,000 m roll tells you the treatment is decaying, and no amount of ink adjustment will cover for it.
Heat. BOPP softens well below the temperatures a PET label shrugs off. If the pack is hot-filled, pasteurised, or lives near a heat source, BOPP-based synthetic sheet is the wrong choice and PET is the right one — a 36 µm PET label holds its shape where BOPP would wave.
Curl. Film does not absorb water, but it still curls if it is mismatched to its liner. A thin film on a heavy liner curls face-out because the construction is unbalanced; a cavitated film on a light glassine can wrinkle in the roll. Match caliper to liner grammage rather than buying the cheapest liner available.
Die cutting. Cavitated film is compressible, so the depth window between cutting the label and cutting through the liner narrows. Converters who run paper at speed often have to ease pressure and slow slightly for pearlised stock — a converting cost that never appears in the material quote.
Cost. Synthetic facestock generally costs more per square metre than a coated paper of the same caliper, and the difference is largest on the cast mineral-filled route. The justification has to be a real failure mode, not a preference for "plastic lasts longer".
| Symptom on the pack | What is actually happening | Change this first |
|---|---|---|
| Edges lift after a week in the cold chain | Facestock took up water; the adhesive is being blamed for a paper problem | Move to a fibre-free facestock before changing adhesive |
| Label waves or blisters after hot filling | BOPP softened; the film is below its service temperature | Switch to PET, not to a thicker BOPP |
| Ink rubs off in the case | Surface energy below the 36–38 dyn/cm anchor threshold, or contamination | Verify dyne level across the roll, then treat or topcoat |
| Die cut leaves a ragged edge or cuts through | Cavitated film compressed under the blade, narrowing the depth window | Ease pressure and re-set depth; do not thin the liner to compensate |
| Label curls off the liner on the press | Facestock and liner calipers are unbalanced | Rebalance the construction, not the unwind tension |
A specification a mill can quote against needs six lines: facestock route and caliper in microns, face treatment, adhesive chemistry and coat weight, liner grammage, and web width with core size and winding direction. Add the print process and the service temperature, because those two decide whether the answer is BOPP at all.
Our own line coats and laminates at 1,080 mm and runs at up to 180 m/min, and every lot goes through five checks before it ships: initial tack, holding power, 180-degree peel, climate ageing and coating appearance. Minimum order is 1,000 m2, lead time is 15 to 25 days, and samples with a TDS go out before the order.
One thing worth stating plainly: we run BOPP and PET film facestocks, including white opaque and cavitated (pearlised) grades, and we coat glassine liners as stock. We do not produce cast mineral-filled synthetic sheet of the heaviest-filled type. If your job genuinely needs that hand and that print behaviour, we will tell you rather than substitute a cavitated BOPP and let you find out on press.
Answered by the coating and conversion team, not by marketing.
Six surfaces, 25 to 100 µm — where white opaque, clear, matte and pearl sit against each other.
Surface choice changes ink lay, scuff resistance and how a barcode reads under directional light.
Aqueous inkjet needs somewhere for the ink to go; on film that is a coating, not a treatment.
When the service temperature rules BOPP out, PET is the answer — and it weighs about 50% more.
Cold chain combines a water problem with a low-temperature problem; the facestock is only half of it.
How a 1,000 m² minimum works in practice and what ships with a trial quantity.