Non-Woven Bag GSM Guide: How to Choose the Right Fabric Weight

Two quotations arrive for the same custom non-woven bag, both marked 90 gsm, same size, one clearly cheaper. When the samples land, the cheaper bag feels like a leaflet with handles, and neither document was false. gsm alone does not describe a fabric closely enough to compare.

Weight sets the floor on cost, predicts less than buyers assume, and is the line most often quietly shaved between quotation and shipment.

What gsm measures — and what it does not

gsm is grams per square metre: the mass of one square metre of fabric, an areal density rather than a thickness, a strength or a grade. ISO 9073-1 and ASTM D3776 weigh a conditioned specimen of known area and scale it up — the whole definition, and the trap, because two fabrics can weigh the same and behave nothing alike.

Filament fineness is one reason: finer filaments give more filaments per gram, better cover and higher tensile at the same weight. Bonding is another, engraved calender rollers fusing filaments where their raised points touch, so a large bonded area gives a stiff, papery cloth with poor tear resistance and small widely spaced dots a soft, drapey one — see how the fabric and the bag are made.

The third reason costs money: polypropylene has a density of about 0.905 g/cm3 and calcium carbonate filler around 2.7, so a filled fabric reaches nominal weight with less polymer doing structural work. A heavily filled 90 gsm can be weaker and more brittle than a clean 75 gsm while weighing exactly what the datasheet claims, so gsm belongs beside tensile values, not instead of them.

How to check gsm yourself, properly

Cut 10 cm × 10 cm with a template and blade — 100 cm2 — weigh it on a balance reading to 0.01 g and multiply the grams by 100: a 0.82 g specimen is 82 gsm. A square cut a millimetre generous on two sides reads 2% light, and an 80 gsm specimen weighs only 0.8 g, so cut ten, stack them and divide.

One specimen is not a measurement. Areal density varies across the web and drifts along the roll, and edges are least representative. Take five or more specimens from several bags and cartons, avoid print, hems, welds and handle overlaps, and report the mean and the spread: 90 with a range of 12 is a different purchase from 88 with a range of 3.

Humidity matters less than expected, because polypropylene is hydrophobic; what takes up water is the filler and finishes, plus condensation on samples from a cold container. Labs condition at 23 degrees Celsius and 50% relative humidity under ISO 139; in an office, unwrap the sample for a few hours and weigh control and production on one balance in one session. Better still, weigh specimens from the sealed signed sample and the shipment together, so calibration and template tolerance drop out.

Why gsm does not predict thickness, opacity or strength

Thickness. The web is compressible, so calliper needs a stated pressure, 0.5 kPa under ISO 9073-2, and a lightly bonded 70 gsm can measure thicker than a hard-calendered 90 gsm while testing weaker.

Opacity. Hiding power is optical, driven by fibre surfaces and pigment: a navy 60 gsm conceals contents better than a white 90 gsm, so pigment beats mass where the brief is “not see-through”.

Tensile. Results under ISO 9073-3 rise sub-linearly and are direction-dependent, machine direction typically one and a half to two and a half times cross direction, which makes panel orientation on the layout a real decision.

Tear and bursting. Here it inverts: bursting under ISO 13938-1 and tear under ISO 9073-4 need filaments free to share load, so as bonded area rises tensile improves while tear falls. And bags rarely fail mid-panel, but at the handle root, base seam or crease.

The four working weight bands

Mills run standard weights, and asking for 85 gsm where the line runs 80 and 90 can cost more than the next step up.

40–60 gsm — handouts, inner bags, dust covers

Light, soft, translucent and cheap, carrying a couple of kilograms of flat contents before the handle root gives way. Good for handouts, garment carriers, dust bags and single-piece styles such as d-cut and vest-handle bags, since a wide gusset in 50 gsm collapses. Print one or two bold spot colours: ink ghosts through and small type loses its edges. It reads as disposable — honest for a handout, wrong once the bag must be reused.

70–90 gsm — the working default

Most volume sits here, 80 gsm being the reference for supermarket carriers and conference bags: a normal grocery load and repeated trips, provided the handle root is reinforced. Most of the reusable shopping bag range is quoted in this band, and screen printing behaves predictably at four to six spot colours. Ten more gsm buys less perceived quality than lamination or a better handle. Wrong choice when the bag must stand square unsupported.

100–120 gsm — retail carriers and gift bags

Structured, stiff enough to stand up empty, and where a customer’s hand registers “quality”: 90 to 110 gsm is the most noticeable jump in perceived value. Home of boutique carriers, box bags and rope handles, usually laminated. The limit shifts onto handle attachment and base, so a board insert and reinforced root become normal, and load-bearing seams are better sewn. Wrong for a mass give-away, or contents that must breathe.

130–160 gsm and above — heavy duty and near-textile

Stiff, costly and bulky to ship. Some fabrics sold in this range are needle-punched or stitch-bonded rather than spunbond, which changes surface and print behaviour, so ask what the construction is. Sewn seams, webbing handles and a rigid base insert are normal, and the fabric supports tool bags and sample cases. The caveat is appearance: an 8 oz canvas tote is roughly 270 gsm of woven cotton and looks like it, so if the brief is hand-feel rather than load, price canvas too.

What gsm really does to unit cost

Fabric cost is close to proportional to weight: 80 to 100 gsm is 25% more polymer over the same layout. Unit price, though, is fabric plus costs that barely move with weight. Cutting waste follows bag geometry; printing follows colour count and run length, so screens and setup cost the same at 70 or at 120; forming labour per bag is roughly constant, rising at both ends since light fabric registers badly and heavy fabric welds slowly.

Freight is the forgotten line: these are low-density goods, charged on volumetric weight by air and constrained by cubic metres at sea, so thicker fabric means fewer bags per carton. Ask for carton count, dimensions and total volume at both weights, not only the unit price.

So the marginal return falls away quickly. From 60 to 80 gsm you buy function; from 90 to 110 you buy perception, rational for a retail carrier; from 120 to 140 most recipients cannot tell without both bags in their hands. Before approving the last increment, price a reinforced handle root, a base board or lamination instead.

Lamination changes the gsm arithmetic

This is the most expensive misunderstanding in the category. The gsm on a quotation normally describes the spunbond substrate alone; BOPP film is specified separately, in microns, and is not in that number. A 12 µm film contributes roughly 11 gsm and an 18 µm film roughly 16. Some suppliers quote the finished laminate, so a bag sold as “90 gsm laminated” may sit on a 75 gsm substrate. Ask in writing which convention applies.

Film also adds stiffness out of all proportion to its mass, a continuous, biaxially oriented layer sitting where bending stress is greatest. A laminated 80 gsm bag stands on a shelf roughly as a plain 100 gsm one does, so if you are reaching for weight because the bag looks unimpressive empty, lamination is the cheaper lever. Much of the laminated non-woven range uses lighter substrate for that reason.

What film does not add is load capacity, since handle tear-out and seam failure are unaffected. Hence an order of judgement: for stiffness, appearance, water resistance or print quality, consider lamination before weight; for load or tearing in service, weight and construction are the answer; if the contents must breathe, lamination is off the table and gsm is your only lever. Our comparison of laminated against unlaminated construction covers the rest.

Joining method and gsm are coupled

Ultrasonic welding fuses the fabric to itself with vibration and pressure, and the process window — amplitude, pressure, dwell, anvil pattern — is set against fabric mass. It narrows sharply at low weight: below about 60 gsm, too little energy and the seam peels, too much and the horn burns through or leaves a brittle join that cracks the first time the bag is folded. Heavy fabric needs more energy per unit length, so above roughly 120–130 gsm many converters move load-bearing seams to stitching; our note on welding against stitching sets out how to choose.

The handle root is the highest-stress point in any bag, and its reinforcement must rise with the fabric, because a heavier bag invites people to put more in it. A folded patch, a doubled hem or a box stitch through the root costs less than 20 gsm across the bag and does more for survival.

What gsm does to print

On light fabric, screen ink ghosts through to the reverse, wet ink wicks along filaments so fine lines gain weight, and the web distorts under squeegee pressure. Heavier fabric is flatter and more stable, so edges are crisper and light inks cover better. Two things are weight-independent: photographic and four-colour work is printed by rotogravure onto film and then laminated, because no screen print holds a smooth gradient on fabric; and printability depends on corona treatment, which decays in storage, so old stock prints badly however heavy it is.

Under-weight fabric, tolerances and the clauses that prevent it

Quoting 90 gsm and shipping 75 is a long-established way to hit a price target: the blunt version substitutes a lighter roll and hopes nobody cuts a specimen; the subtler one delivers nominal weight with filler, so the balance reads correctly and the tensile does not.

So write the number properly. State nominal gsm with a tolerance — mills generally work to about plus or minus 5%, and 3% is achievable on a well-controlled line — name the test method, ISO 9073-1 or ASTM D3776, the specimen area and count, and that the mean governs, not any single reading. Say whether a laminated weight is substrate or composite, and name the reference: a signed, dated counter-sample plus the mill’s roll certificate of areal density per lot.

AQL 2.5 major / 4.0 minor at general inspection level II under ISO 2859-1 is the usual default, and right for visual defects and dimensions, but it is attribute sampling and areal density is a variable. Specify it separately: destructive specimens per lot from different cartons, tested for gsm, tensile in both directions and handle pull, with pass criteria beside the AQL clause.

A specification naming these fields will get comparable numbers from any supplier:

• Substrate — spunbond polypropylene, nominal gsm, tolerance, test method, filler limits.
• Whether that gsm is substrate or laminated composite — in words, not implied.
• Mechanical requirements — tensile in both directions, rated load for the bag.
• Lamination — film type, thickness in microns, gloss or matte.
• Print — method, colour count, Pantone references with coated or uncoated suffix.
• Size — width × height × gusset, with the measurement conventions agreed.
• Handles — type, length, width, attachment, root reinforcement.
• Construction — welded or sewn, seam allowance, base insert.
• Packing — count per inner, carton dimensions, total volume.
• Inspection — sampling standard, AQL levels, destructive test plan, sample number.

Working back from the use case to a weight

Derive the number from the job rather than from a figure someone quoted at you.

1. Load. Weigh the heaviest realistic contents, not the intended contents; that sets the floor for fabric mass and dictates handle and base construction.
2. Reuse. A handout has no durability requirement; a bag meant for repeated trips needs mass and a reinforced root.
3. Print complexity. Photographic or four-colour artwork forces a laminated construction, so settle the artwork first.
4. Lamination. Decide it before final gsm, since film substitutes for roughly 20 gsm of stiffness, and rule it out if the contents must breathe.
5. Geometry. A tall panel with a wide gusset needs more stiffness than a flat d-cut of the same capacity.
6. Brand perception. Must the bag stand square and empty in front of a customer? That is stiffness: 100 gsm and above, or lamination.
7. Budget. Check the freight consequence, then ask whether the last increment beats the same money spent on the root or the film.

When we would tell you not to go heavier

We will be direct about where extra weight is wasted money. If the bag is a genuine single-use handout, mass is material the recipient never notices. If the contents must breathe, you cannot laminate and a denser fabric makes it worse. If bags are failing at handles or seams, weight will not help: the failure is at the join.

Where the requirement is “not see-through”, pigment is cheaper than mass; where it is “stands up on the shelf”, lamination or a base board is cheaper than 20 gsm. And if you are going heavier because a previous order arrived under-weight, that is the wrong fix — put a tolerance, a test method and an incoming check in the order instead.

If you would rather not guess, tell us the load, the contents, the artwork and the destination market through our quotation form, and ask for two weights quoted side by side with carton counts and volumes for both. We usually reply within one business day.

Frequently asked questions

How can I check the gsm of a non-woven bag myself?

Cut a 10 cm × 10 cm specimen, which is 100 cm2, weigh it and multiply the grams by 100. Stack ten specimens and divide to suppress cutting and balance error, take them from several bags and cartons, and avoid print, welds and hems.

Why do two bags with the same gsm feel completely different?

Because gsm is only mass per square metre. Filament fineness, the calender bond pattern and calcium carbonate filler all change hand-feel, stiffness and strength at identical weight, so a heavily filled 90 gsm fabric can be weaker than a clean 75 gsm one.

Does lamination count towards the gsm figure?

Normally not. The quoted gsm is the spunbond substrate, while BOPP film is specified separately in microns, and 12 µm film adds roughly 11 gsm. A bag sold as 90 gsm laminated may sit on a 75 gsm substrate, so ask which convention applies.

What gsm should I use for reusable grocery bags?

The 70–90 gsm band, usually 80, takes a normal grocery load and repeated trips. The deciding factor is rarely the last ten gsm: handle root reinforcement, the base seam and the gusset govern whether the bag survives.

What gsm tolerance should my specification state?

Nominal weight plus or minus 5% is normal mill practice, and 3% is achievable on a well-controlled line. Name the test method, specimen area and count, state that the mean governs, and add a destructive test plan, since attribute sampling does not cover a variable like areal density.

Buyer Summary

GSM describes fabric mass per square metre, but it does not define the complete bag strength. Specify GSM together with dimensions, seams, handles, reinforcement and a representative load test.

Related Sourcing Resources

• Browse non-woven bag formats
• Ask for a GSM-based quotation

Frequently Asked Questions

What does GSM mean for a non-woven bag?

GSM is grams per square metre and describes the nominal weight of the fabric before it becomes a finished bag.

Does higher GSM always mean a better bag?

No. The correct weight depends on use, load, appearance and budget, while seams and handles also control performance.

How can buyers verify GSM?

Agree the test method and tolerance, then check production fabric by weighing a measured area or using an equivalent documented procedure.

Prepared by the Global Bag Supply sourcing team · Updated August 8, 2026