If you import fiberglass mesh — whether for insect screening, wall reinforcement, or EIFS applications — you receive specification sheets from suppliers every day. Some are detailed. Some are suspiciously thin. And some contain numbers that look impressive but mean nothing in practice.
Knowing how to read a fiberglass mesh specification sheet is one of the most underrated skills in B2B sourcing. A small misinterpretation of one parameter can lead to a container of mesh that underperforms, fails inspection, or disappoints your customers.
In this article, we break down the key specification parameters for fiberglass mesh, explain what each number actually means, highlight common supplier tricks, and give you a practical checklist for evaluating any spec sheet.
1. The Core Specification Parameters
Every fiberglass mesh specification sheet should include the following parameters. If any are missing, ask why.
| Parameter | Unit | What It Tells You | Why It Matters |
|---|---|---|---|
| Mesh Count | ends × picks / inch (or / 25 mm) | Number of warp and weft yarns per unit length | Determines opening size, coverage, and strength distribution |
| Grammage (Weight) | g/m² | Total weight per square meter (yarn + coating) | Directly affects strength, coating coverage, and cost |
| Yarn Type | — | Fiberglass type (C-glass, E-glass) and tex count | Determines base strength and chemical resistance |
| Coating Type | — | PVC, acrylic, urea-formaldehyde, or blend | Controls alkali resistance, UV stability, flexibility, and color |
| Coating Content | % (by weight) | Percentage of total weight that is coating material | Higher coating = better protection; too high = stiff mesh |
| Tensile Strength | N/5 cm | Breaking force in both warp and weft directions | The most important mechanical performance indicator |
| Alkali Resistance | % retention | Residual tensile strength after 28-day NaOH immersion | Critical for any mesh used with cement-based materials |
| Roll Width | cm or m | Usable width of the mesh roll | Must match your cutting and application requirements |
| Roll Length | m | Length per roll | Affects handling, shipping efficiency, and per-unit pricing |
These nine parameters form the foundation of any serious fiberglass mesh purchase. Let’s examine the ones that cause the most confusion among importers.
2. Grammage: The Most Misunderstood Number
Grammage — weight per square meter — is often the first number buyers look at. It is also the most frequently manipulated.
What grammage actually measures: The total weight of both the glass fiber yarn and the applied coating per square meter. Two meshes can have identical grammage but completely different compositions.
Example:
| Scenario | Yarn Weight | Coating Weight | Total Grammage | Real-World Performance |
|---|---|---|---|---|
| A: Proper balance | 120 g/m² | 25 g/m² | 145 g/m² | Strong mesh, good protection |
| B: Heavy coating trick | 95 g/m² | 50 g/m² | 145 g/m² | Looks identical on scale, but much weaker core — coating masks low yarn weight |
| C: Underweight | 110 g/m² | 20 g/m² | 130 g/m² | Reported as 145 g/m² — 10% under specification |
How suppliers manipulate grammage:
- The coating trick: Increasing coating weight to hit a grammage target while using lighter, cheaper yarn. The mesh feels heavy but tears easily because the glass fiber core is weak.
- The moisture trick: Mesh stored in humid conditions absorbs moisture, artificially inflating weight. The grammage drops after the mesh dries out in your warehouse.
- The tolerance game: Quoting nominal grammage of 145 g/m² but delivering rolls that consistently weigh 135–138 g/m² — within a “generous” 10% tolerance they wrote into the fine print.
Buyer’s checklist for grammage:
- Ask for grammage broken down by yarn weight and coating weight — not just the total.
- Specify your acceptable tolerance (±3% is reasonable for professional manufacturing; more than ±5% is a red flag).
- Weigh sample rolls yourself when they arrive. Use a calibrated digital scale and cut a 100 cm × 100 cm sample.
- Compare grammage of retention samples against subsequent shipments to catch drift.
3. Tensile Strength: The Performance Number That Counts
If grammage is the most quoted number, tensile strength is the most important number. It tells you how much force the mesh can withstand before breaking — and it reveals whether the yarn and coating are doing their job.
Standard test method: ISO 13934-1 (strip method). A 50 mm wide strip of mesh is clamped and pulled until it breaks. The result is reported in N/5 cm, separately for warp (lengthwise) and weft (crosswise) directions.
What affects tensile strength:
- Yarn tex (linear density): Heavier yarn = higher strength. This is the primary driver.
- Mesh count: More yarns per inch = more load-bearing fibers = higher strength.
- Coating quality: A coating that bonds well to the glass fibers distributes load across multiple filaments, improving effective strength.
- Weave structure: Leno weave (used for insect screen) has different strength characteristics than plain weave (used for wall mesh).
Typical tensile strength ranges for common products:
| Product Type | Typical Grammage | Warp Strength (N/5 cm) | Weft Strength (N/5 cm) |
|---|---|---|---|
| Insect Screen (18×16 mesh) | 120–130 g/m² | ≥ 180 | ≥ 160 |
| Insect Screen (16×14 mesh) | 100–105 g/m² | ≥ 140 | ≥ 120 |
| Wall Mesh (5×5 mm, 145 g/m²) | 145–150 g/m² | ≥ 1200 | ≥ 1100 |
| Wall Mesh (4×4 mm, 160 g/m²) | 160–165 g/m² | ≥ 1500 | ≥ 1400 |
| EIFS Reinforcing Mesh (145 g/m²) | 145–150 g/m² | ≥ 1300 | ≥ 1200 |
Red flags in tensile strength claims:
- Strength values that are significantly higher than industry norms for the stated grammage
- Warp and weft strength that are suspiciously identical (natural variation means they should differ slightly)
- No test standard referenced — just a bare number with no context
- Only one direction reported (usually the stronger warp direction)
4. Alkali Resistance: The Hidden Differentiator for Wall Mesh
If you import fiberglass mesh for plaster reinforcement, EIFS, or any application involving cement, alkali resistance is the single most critical performance parameter. Ignore it at your peril.
The problem: Portland cement has a pH of 12–13 — highly alkaline. Bare glass fibers (especially E-glass) are chemically attacked by alkali, losing strength rapidly. Within months, unprotected mesh embedded in cement can lose 60–80% of its original tensile strength.
The solution: A protective coating — typically PVC, acrylic, or a specialized alkali-resistant formulation — that shields the glass fibers from the alkaline environment.
Standard test: ETAG 004 / ISO 10406-1. Mesh samples are immersed in 5% NaOH solution at 23°C for 28 days. The residual tensile strength is then measured. The pass criterion is ≥ 50% strength retention.
What the numbers mean in practice:
| Strength Retention After 28-Day NaOH | Interpretation | Suitable Application |
|---|---|---|
| ≥ 70% | Excellent — professional-grade coating | EIFS, structural plaster, permanent formwork |
| 50–69% | Acceptable — meets ETAG 004 minimum | Standard plaster reinforcement, general construction |
| 30–49% | Marginal — borderline compliance | Temporary applications, non-critical use. Not recommended for structural. |
| < 30% | Fail — inadequate protection | Do not use with any cement-based materials |
Buyer’s checklist for alkali resistance:
- Always request alkali resistance test reports — not just a statement claiming compliance.
- Check which standard was used (ETAG 004 is the most rigorous and widely recognized).
- Ask for the residual strength percentage, not just a pass/fail result. One supplier’s “pass” at 51% retention is very different from another’s 75%.
- For critical applications, request a third-party test from SGS, Bureau Veritas, or Intertek.
- If the supplier cannot provide any alkali resistance data for wall mesh, walk away.
5. Specification Traps: Common Tricks and How to Spot Them
After years of auditing supplier specifications, we have catalogued the most common tactics used to make mediocre mesh look competitive on paper.
| Trick | What It Looks Like | How to Protect Yourself |
|---|---|---|
| The “Nominal” Gambit | Spec says “145 g/m² nominal” — but the fine print allows ±10% tolerance. You pay for 145, you get 131. | Specify a tight tolerance in your purchase order: grammage ±3%, roll length 0/+2%. |
| The Missing Direction | Tensile strength reported only for warp (stronger direction). Weft is 30–40% lower but not disclosed. | Demand both warp AND weft values on every tensile test report. |
| The Sample Swap | Pre-production sample is excellent. Production shipment is inferior — but you approved based on the sample. | Retain sealed reference samples. Perform AQL sampling on every shipment against the retained sample. |
| The Coating Swap | Sample uses expensive acrylic coating. Production switches to cheaper UF (urea-formaldehyde) — looks similar, performs worse. | Specify coating chemistry in the contract. Test coating type with simple burn-off or solvent test on arrival. |
| The Phantom Certification | Supplier claims ISO 9001 or CE marking but cannot produce a valid certificate from an accredited body. | Verify certifications independently. Ask for the certificate number and issuing body, then check. |
| The Round-Up Game | Mesh count is 17.2 × 15.6 per inch — rounded up to “18×16” on the spec sheet. | Count mesh yourself with a pick glass on arrival samples. ±0.5 is normal; ±1.0 is questionable. |
6. Building Your Internal Spec Sheet Template
The best defense against specification confusion is a standardized internal template that every supplier must complete — in the same format, with the same units, referencing the same test standards.
Here is the minimum information your template should capture for each product inquiry:
- Product description: Application, weave type, intended use
- Mesh count: Ends × picks per inch (or per 25 mm), measured per ASTM D3775
- Grammage: Nominal g/m², yarn weight component, coating weight component, tolerance
- Yarn specification: Glass type (C-glass or E-glass), tex per yarn
- Coating specification: Chemistry type, coating content as percentage by weight
- Tensile strength: Warp and weft, N/5 cm, tested per ISO 13934-1
- Alkali resistance: Residual strength % after 28-day NaOH, tested per ETAG 004 (for wall mesh only)
- Roll dimensions: Width (mm), length (m), core diameter, maximum roll diameter
- Packaging: Inner wrap, outer wrap, palletization, labeling requirements
- Color: RAL or Pantone reference if color matching is required
- Test reports: In-house or third-party, date of most recent test
When every supplier fills out the same template, comparing offers becomes straightforward — and specification tricks become obvious.
Key Takeaway
A fiberglass mesh specification sheet is not just a formality. It is the technical contract between you and your supplier. Every number on that sheet affects the product your customer receives and the reputation you carry in your market.
Learn to read specifications critically. Ask for breakdowns, not just totals. Reference test standards by name. And never accept a number you cannot verify.
The best suppliers welcome detailed specification discussions because they have nothing to hide. If a conversation about specs makes your supplier uncomfortable, that discomfort is information.
Want to see how CredenTex structures its product specifications? Contact us and we will share our full technical data sheets for any product in our range — with every parameter disclosed and every test standard referenced.