What Are the Differences Between the FS, FM and FG Density Series? Softness, Stiffness and Opacity Compared

What Are the Differences Between the FS, FM and FG Density Series? Softness, Stiffness and Opacity Compared

FS, FM and FG are the three Flexstone® film and sheet density series. The two-letter prefix on the part number is the density: FS is 1.0 g/cm³ and is described as soft, lightweight and paper-like; FM is 1.2 g/cm³ and is the balanced series; FG is 1.4 g/cm³ and is described as stiff. Choose the prefix for hand-feel and rigidity at the thickness the job needs. That is the decision the letters answer.

Opacity is not a density-series property, and neither are gloss, temperature rating or the print-process list. Those are published by part-number group. A higher density does not buy more hiding power, a 120 °C short-term rating, or a press compatibility. Published figures below are tagged to the group or specification sheet they come from. Calculated masses are tagged as nominal arithmetic. None of them can be carried across the series.

Side-by-side:

FS, FM and FG across density, feel, nominal weight and published opacity

Density, published hand-feel and nominal basis weight differ by series; opacity does not, and the lowest published opacity floor in this set sits on an FG grade, not on FS.

These minima are specification floors, not measured series averages. FG-2K15’s published minimum (≥85%) is lower than the minimum for FS-2K20–30 (≥95%). That shows density is not hiding power. It does not prove that every FG sheet hides less than every FS sheet.

Wall-fabric composites (NMEQS-MACO 299) are a separate construction. Rolls are 50 m × 1500 mm. Opacity is the grade figure above (FS wall-fabric ≥95%, FM wall-fabric ≥92%). Basis weight is the figure on that sheet, not the bare-film formula. K-coated wall-fabric on that sheet is listed for wide-format UV inkjet; confirm the coating on the specific grade before locking the process. Grade-prefix rules are set out in Flexstone grades and part numbers.

These three prefixes apply to Flexstone film and sheet. Pellet grades are a separate PP/PE series — inorganic content more than 60%, density about 1.5 g/cm³ — and are not FS, FM or FG. Do not copy film opacity or temperature onto pellet, or pellet mechanics onto film.

Nominal basis weight follows one formula, so the density series shows up directly in grams per square metre

At the same thickness, nominal basis weight scales with series density, so FG is 40% heavier per square metre than FS and FM is 20% heavier than FS.

Formula 1 — nominal basis weight. For non-adhesive grades, nominal basis weight (g/m²) ≈ thickness (mm) × density (g/cm³) × 1000. At 0.20 mm that is 200 g/m² (FS), 240 g/m² (FM) and 280 g/m² (FG). At 0.35 mm it is 350, 420 and 490 g/m². Do not apply the formula to self-adhesive constructions, where total thickness differs by part number, or to wall-fabric composites.

FG at 1.4 g/cm³ is 40% heavier than FS at the same thickness (1.4/1.0 − 1). Area per tonne moves the other way: FG gives 1.0/1.4 of the FS area, which is 28.6% less area per tonne, not 40% less. If a quotation, freight bill or payload is calculated per kilogram, the series is a mass decision as well as a hand-feel decision. No selling price is stated here.

Formula 2 — roll mass, nominal arithmetic only. Roll mass (kg) = basis weight (g/m²) × width (m) × length (m) / 1000. A published wide-format inkjet roll of 1270 mm × 50 m covers 63.5 m². At 0.20 mm non-adhesive nominal basis weight that is 12.7 kg in FS and 17.78 kg in FG, a 5.08 kg difference on this nominal calculation. These are not weighed production rolls. For specification-sheet grades, shipped mass follows the tolerance on that part number’s sheet. Brochure-only grades have not published a tolerance. Wide-format inkjet rolls are also published at 1370 mm and 1524 mm; scale mass with width. Do not reuse this 1270 mm × 50 m calculation for narrow label stock (210 / 310 / 410 / 510 mm) or for wall-fabric (1500 mm).

No bending-stiffness coefficient, tensile strength or elongation is published as an FS, FM or FG series value. The published distinction is the hand-feel descriptor. Tensile strength and elongation, where published, belong only to FS/FG 2K at 0.15–0.30 mm (NMEQS-MACO 293). Read them on that sheet. Do not copy them onto FM, onto 0.35 mm, or onto other coatings. If the job is stiffness-critical or weight-critical, fix both thickness and series, then confirm handling on a sample.

Spec and process windows are published per part-number group, never per density series

Print process, gloss and temperature are published by part-number group. A density prefix does not transfer them, and the same coating letter does not mean the same process list in every series.

Unqualified “2K” means offset and UV only. Unqualified “2I” means HP Indigo only. “UV” is two processes: wide-format UV inkjet, or UV-curing ink on a press. They are not interchangeable.

FS/FG 2K at 0.15–0.30 mm lists more processes than brochure-only FM-2K and 0.35 mm 2K. FG digital-press grades list more processes than brochure-only FS-2I and FM-2I. Moving from FS to FG does not add or remove a process; the part-number group does.

Gloss and whiteness are group data, not a series ranking. Published whiteness for specification-sheet grades is ≥82 for most grades; FS-2K30 and FG-2K30 are ≥84. There is no series split in the grade data. Gloss is 3–8° on S-coated grades and on FG 2I/I grades; 9–12° on K-coated grades; and 4–6° / 9–12° on FS/FG 2K at 0.15–0.30 mm (NMEQS-MACO 293). Brochure-only grades publish nominal basis weight only — no gloss or whiteness.

Temperature data exist for exactly two groups, and they are not a series or coating limit. FS/FG 2K at 0.15–0.30 mm (NMEQS-MACO 293): long-term (days) 80 °C; short-term (minutes) 100 °C for FS and 120 °C for FG. FG digital-press grades (NMEQS-MACO 298): long-term 80 °C, short-term 120 °C. No other grade has a published temperature rating. Do not write “120 °C” or “heat resistant” against Flexstone, a density series, or a coating. For grades with no published rating, say that temperature data are not published and that the grade is not for high-temperature retort or other extreme-heat processes. Test before any heating step.

For grades covered by specification sheets, press-room relative humidity is 30–60% RH. Store in the original packaging, out of direct sunlight, at 20–70% RH; shelf life is 12 months. Press-room temperature and storage temperature are published on the specification sheet for the part number, not as one window for every grade and not as an FS, FM or FG series limit. Do not merge temperature figures from different sheets. Read NMEQS-MACO 293–299 or 303 (revision A0) for the grade in hand before setting the press room or the store. The in-use environment — the finished piece, not the press window and not a temperature rating — is −20 °C to 60 °C and 20–80% RH, with less than 15 °C change within 30 minutes. Reseal unused material. Specification sheets other than NMEQS-MACO 293 also require leftover material to be used within one month. Brochure-only grades have not published these conditions; do not copy them across.

Where Flexstone — and a given density series — is the wrong choice

Outdoor duration, fire rating, clarity, extreme heat and end-of-life claims sit outside what a density prefix can specify.

Outdoor durability is lower than PVC. Do not specify Flexstone for long-term exterior signage. Short-term outdoor posters are within the intended range. No outdoor service life in months or years is published here; do not add one. Do not describe the material as outdoor-durable, weatherable or UV-resistant.

Applications with a strict fire rating still need flame-retardant PVC. A halogen-free flame-retardant formulation is still in development. Do not specify current catalog grades as fire-resistant, flame-retardant or fireproof.

Catalog grades are warm white and opaque. They cannot replace a clear film. They are denser than PP pearl film and therefore heavier per unit area. Inside the range, do not specify FG when the constraint is mass, or FS when the constraint is stiffness. FM does not split that difference with a published stiffness number.

The material contains thermoplastic resin. It is not for high-temperature retort or other extreme-heat processes, in any series. PET remains the appropriate choice there. The short-term 100 °C and 120 °C figures above are not a retort rating and do not apply outside their two groups.

Flexstone is not described as biodegradable or compostable. Published end-of-life routes — Newlife product information, not a third-party life-cycle assessment — are pulverising and re-forming, and energy recovery (incineration). Post-consumer collection depends on local sorting and the recycler.

No food-contact compliance, medical use, or other certification is stated here. Do not infer one from the density series or from a company-level description. A certification applies only when the specification sheet for that part number states it.

The specification sheets, samples and press trials behind these numbers

Published numbers stop at the named sheet. A gap on one group is not filled by copying another series.

Figures in this guide are product data from Guangzhou Newlife New Material Co., Ltd. (Newlife) for Flexstone: specification sheets NMEQS-MACO 293–299 and 303 (revision A0), the Flexstone brochure and product sheets, and the grade and part-number rules. Calculated roll masses are nominal arithmetic, not weighed stock. Where a group has no published opacity, gloss, mechanics, temperature or storage data, this guide does not extrapolate. Specification-sheet PDFs are on the downloads page.

Before a production run, trial on your equipment anything the sheet does not settle: adhesion and cure with your ink, cutting and creasing at your thickness in the series you chose, adhesive behaviour on your surface, and any finishing step the published data do not cover, including laminating, foiling, or a named ink brand. A small sample is the check. A density prefix is not.

Buyer questions on FS, FM and FG

Is FS always the most opaque series? No. Opacity is published by part-number group, not by series. FS-2K20–30 and FS wall-fabric grades are ≥95%, FM wall-fabric grades ≥92%, FG-2K15 ≥85%, and other specification-sheet grades ≥90%. Brochure-only grades, including FM-2K, FM-2I and FS-2I, do not publish opacity.

Can I get FG stiffness at FS weight? Not at the same thickness. Nominal mass scales with density, so FG is heavier than FS at equal thickness. No series-wide stiffness coefficient is published, so saving weight by reducing thickness is a sample decision, not a calculated equivalent.

Which series for a dry-toner digital press? Not a series. Specify the FG digital-press grades FG-2I, FG-I15-PSA and FG-I20-PSA (NMEQS-MACO 298). The FS/FG 2K group on NMEQS-MACO 293 is not HP Indigo compatible, and dry-toner equipment needs a test before that group is used. Brochure-only FS-2I and FM-2I are HP Indigo grades with nominal basis weight only.

Does a higher density series print differently? Print-process capability is tied to coating and part-number group, not to FS, FM or FG. Check that group’s process list, and state whether “UV” means wide-format UV inkjet or UV-curing ink on a press.

Which series for wallcovering? Do not pick it from the bare-film formula. Wall-fabric composites publish basis weight and opacity by grade on NMEQS-MACO 299: FS wall-fabric grades ≥95%, FM wall-fabric grades ≥92%. Confirm the coating on the specific grade before locking the press. See wallcovering substrates.

Next steps: specify the series on evidence, then run a sample

Send the press and ink type (HP Latex, wide-format UV inkjet, UV-curing ink on press, offset, flexo, screen, HP Indigo or dry toner), the roll width or sheet size, the thickness and density series, whether the construction is self-adhesive and what surface it goes on, and the finished piece’s use environment and expected service life. Use the material comparison page when the alternative is PVC, PP pearl film or another substrate, and follow the selection sequence in choosing a substrate. Contact the Flexstone application engineering team for samples and the specification sheet behind each number: request samples and specification sheets.

References

1. Guangzhou Newlife New Material Co., Ltd. (Newlife). Flexstone specification sheets NMEQS-MACO 293, 294, 295, 296, 297, 298, 299 and 303, revision A0. 2. Flexstone brochure and product sheets (Flexstone eco-material / stone paper). Guangzhou Newlife New Material Co., Ltd. 3. Flexstone grades and part numbers: https://www.stonepapers.net/en/knowledge-base/flexstone-grades-part-numbers 4. Flexstone stone paper fundamentals: https://www.stonepapers.net/en/knowledge-base/stone-paper-fundamentals 5. Flexstone material comparison: https://www.stonepapers.net/en/compare 6. Flexstone specification-sheet downloads: https://www.stonepapers.net/en/downloads 7. Flexstone product centre: https://www.stonepapers.net/en/products 8. Flexstone Pellet product introduction (PP/PE series; not an FS/FM/FG film grade): https://www.stonepapers.net/en/products/pellet