📌 Key Takeaways
Specification drift—not true price differences—causes 15–20% quote variance that collapses to 3–5% when buyers name test methods and tolerance bands.
- Method-Named Properties Eliminate Interpretation Games: Requesting “kraft linerboard” without defining GSM tolerance, burst test method (ISO 2758 vs TAPPI T 403), and moisture range lets suppliers quote different products that all claim the same nominal spec but perform inconsistently on your line.
- The Matrix Maps Measurable Bands to Fit-for-Use Applications: Sack kraft needs 70–100 GSM with 300–500 kPa burst (ISO 2758), 6–8% moisture, and TEA/tear data for filling pressure resistance—copy these bands directly into RFQ fields instead of vague “suitable for multiwall bags” language.
- Evidence Recency Prevents Trial-Success-Then-Production-Failure: COAs dated within 7–14 days of production with method IDs (ISO 536, 287, 2758, 535), lot-roll mapping, and sampling per ISO 186 turn receiving from investigation into verification—you compare delivered properties against agreed baselines, not re-qualify from scratch.
- Recycled Content Requires Adjusted Targets, Not Rejection: Virgin linerboard at 140 GSM delivering 400 kPa burst translates to recycled specs at 160 GSM targeting 380 kPa—compensate for 15–25% lower strength through slightly heavier basis weight when cost savings justify the material penalty.
- Climate and Lamination Create Edge Cases Requiring Spec Adjustments: PE lamination substrates need 5–7% moisture to prevent blistering, while tropical storage requires Cobb maximums under 40 g/m² as paper equilibrates from tested 50% RH to delivered 80% RH environments.
Spec-first = comparable quotes, faster approval, and predictable line performance.
Converters, QA teams, and procurement professionals sourcing kraft paper will find the application-to-property framework here, preparing them for the detailed specification methodology and evidence requirements that follow.
Specification mismatches cause more procurement headaches than price disputes. A procurement manager receives three quotes for “80 GSM sack kraft,” each claiming identical specs. Yet one supplier’s product tears during filling, another absorbs moisture too quickly, and the third works perfectly. The difference? Each supplier interprets “sack kraft” through their own lens of burst strength, Cobb values, and moisture tolerance. Without a shared framework mapping properties to applications, both parties waste time chasing specifications that never quite align.
This matrix translates measurable kraft paper properties into fit-for-use applications. Instead of iterative back-and-forth or post-award surprises, sourcing teams and suppliers can reference the same property bands and evidence requirements from the start.
What This Guide Covers (and What It Doesn’t)
Verified information from industry standards: The property set below—basis weight, burst strength, tensile properties, tear resistance, Cobb water absorptiveness, and moisture content—represents the core specifications used across kraft paper applications. The ISO and TAPPI test methods referenced are established international and industry standards.
Generally accepted practice: Specifying these properties in RFQs with named test methods enables comparable quotes. Confirming specifications through sampling (per ISO 186) and laboratory testing before scale-up represents standard quality assurance practice in paper procurement.
Illustrative examples: Property ranges and numeric targets shown in the matrix are examples to demonstrate specification structure, not universal requirements. Actual specifications depend on your processing equipment, end-use conditions, and quality tolerances. Validate all targets through trials and supplier capability data.
Why One Matrix Reduces RFQ Chaos and Post-Award Disputes
Quote variance often stems from specification drift rather than actual price differences. When a buyer requests “kraft linerboard” without defining GSM tolerance bands, burst test methods, or moisture ranges, suppliers quote against their internal interpretation. One might assume virgin fiber with ISO 2758 burst testing at 300 kPa minimum, while another quotes recycled content tested per TAPPI T 403 at 250 kPa. Both believe they’ve quoted correctly, yet the products aren’t comparable.
Spec-first RFQs with measurable parameters enable apples-to-apples comparison. When buyers specify “GSM 100 ±3%, burst ISO 2758 minimum 350 kPa, moisture 6–8% per ISO 287,” suppliers can quote precisely and buyers can compare accurately. The variance narrows from 15–20% down to 3–5%, representing actual market differences rather than specification confusion.
This approach prevents renegotiations. A clearly defined property set in the RFQ becomes the acceptance criterion in the contract. Suppliers deliver against known targets, buyers verify against stated methods, and disputes reduce because both parties agreed on measurable specifications before production began.
The Measurable Properties That Actually Decide Fit-for-Use
Kraft paper performance depends on several core properties, each measurable through standardized test methods.
Basis weight (GSM) represents the paper’s mass per square meter. Measured per ISO 536, it affects strength, opacity, and cost. Tolerance bands typically run ±2% to ±5% depending on the application. A 100 GSM specification with ±3% tolerance means acceptable delivery ranges from 97 to 103 GSM. Tighter tolerances cost more but reduce downstream processing variation.
Burst strength measures resistance to rupture under perpendicular pressure. Two primary methods exist: ISO 2758 and TAPPI T 403. Both express results in kilopascals (kPa) for absolute burst, though some specifications use burst index (kPa·m²/g) to normalize for basis weight differences. Testing procedures differ slightly in clamping ring diameter and inflation rate. Virgin kraft typically shows 20–30% higher burst than recycled content at equivalent GSM, though surface sizing can partially compensate. RFQs must name the specific test method since results aren’t directly interchangeable.
Tensile properties measure the force required to break the paper when pulled. ISO 1924-2 and TAPPI T 494 specify constant-rate-of-elongation testing in both machine direction (MD) and cross direction (CD). Results appear as tensile strength (force per width, typically N/m or kN/m) or tensile index (force normalized by basis weight, N·m/g). Tensile energy absorption (TEA) extends this measurement by calculating the energy absorbed during stretching to failure, particularly critical for applications involving sudden stress like drop impacts or filling operations in sack kraft.
Ring crush test (RCT) and edge crush test (ECT) measure compressive strength parallel to the paper surface. These properties matter primarily for corrugated board construction, where linerboard and fluting combine to create vertical stacking strength. For paper tubes and cores, ring compression determines how much radial pressure the structure can withstand during winding or stacking. RCT uses ISO 12192, ECT uses ISO 3037 or TAPPI T 811.
Tear resistance quantifies how much force is needed to continue a tear once started. The Elmendorf method (ISO 1974 or TAPPI T 414) measures this in millinewtons (mN). High tear resistance is essential for sack kraft and retail bags where handling stress concentrates at edges and seams. Tear values are directional—MD and CD tears can differ significantly, particularly in machine-made papers.
Moisture content affects dimensional stability, processing behavior, and mold risk. ISO 287 specifies conditioning at 23°C and 50% relative humidity, with typical kraft paper equilibrating between 6–9% moisture by weight. Higher moisture causes cockling during printing or lamination. Lower moisture makes the paper brittle and prone to cracking during folding. Most specifications set a 2–3 percentage point range to balance processing requirements with dimensional stability.
Air permeability becomes relevant for specific applications like form-fill-seal (FFS) sack kraft, where controlled porosity allows air to escape during high-speed filling without bursting the package. Testing methods vary by application; specifications typically define acceptable ranges rather than single targets.
Cobb test (ISO 535) quantifies water absorptiveness in grams per square meter after 60-second contact. Low Cobb values (below 30 g/m²) indicate good moisture resistance for direct food contact or exterior applications. High Cobb values (above 60 g/m²) suggest uncoated or lightly sized paper suitable for porous bags where air permeability aids filling speed. Intermediate values around 40–50 g/m² serve general-purpose wrapping and inner liners.
Sampling procedures establish how representative test results actually are. ISO 186 specifies sampling locations within production lots, number of test specimens, and conditioning requirements before testing. Proper sampling prevents disputes over whether test results represent the delivered material.
Fiber source and sizing influence all other properties but aren’t directly measured through a single test. Virgin kraft pulp delivers maximum strength and cleanliness, relevant for food-contact grades requiring FDA or EC framework compliance. Recycled content reduces cost but requires careful specification of burst and tensile properties to ensure fitness for use. Surface sizing with starch or synthetic agents improves moisture resistance and printability without changing the base fiber.
Certification requirements add gates beyond physical properties. FSC or PEFC chain-of-custody certificates validate sustainable sourcing claims. Food-contact declarations confirm regulatory compliance with frameworks like FDA 21 CFR 176.170 or EC Regulation 1935/2004. ISO 9001 quality management certification indicates systematic process control. Each certificate requires registry verification—checking the certificate number, entity name, and scope against the issuing body’s online database rather than accepting a document at face value.
Build the Property–Application Match Matrix
The following matrix maps common kraft paper applications to recommended property bands. These ranges represent typical industry practice based on end-use requirements. Actual specifications may vary depending on specific processing equipment, regulatory requirements, or performance targets.
Matrix: Kraft Paper Property–Application Match
| Application | GSM Band | Burst (Method & Min) | Tensile / Tear Context | Moisture (%) | Cobb (g/m²) | Evidence to Request | Notes |
| Kraft Linerboard (Virgin) | 125–200 | ISO 2758: 350–550 kPa or index ≥3.0 kPa·m²/g | Tensile index MD ≥45 N·m/g per ISO 1924-2; ECT per box spec | 7–9% | 25–40 | COA with test cert (7–14 days old) + method IDs | Virgin fiber; may require food contact cert for direct packaging |
| Testliner Board (Recycled) | 100–150 | ISO 2758: 250–400 kPa or index ≥2.5 kPa·m²/g | RCT/ECT critical for board performance | 7–9% | 35–55 | COA + recycled content declaration | Lower burst acceptable; verify no contamination for food proximity |
| Fluting / Corrugating Medium | 80–140 | TAPPI T 403: 200–350 kPa or RCT per ISO 12192 | RCT primary spec; tensile secondary | 7–9% | 40–60 | COA + Concora liner compatibility data | Higher Cobb aids adhesive bonding in corrugator |
| Sack Kraft (Multiwall, FFS, Valve) | 70–100 | ISO 2758: 300–500 kPa | TEA and tear MD/CD per ISO 1924-2, ISO 1974; air permeability per application | 6–8% | 30–50 | COA + valve/pasted end compatibility + air perm data if FFS | Burst + TEA critical for filling pressure; tear resists handling shocks; controlled porosity for de-aeration |
| Retail Bags & E-commerce Mailers | 50–90 | ISO 2758: 200–350 kPa | Tensile MD/CD per ISO 1924-2; tear per ISO 1974 | 7–9% | 35–50 | COA sufficient; add print surface test if graphics critical | Handle strength + puncture resistance; Cobb matters if moisture exposure likely |
| Industrial Wrapping Paper | 50–80 | TAPPI T 403: 150–250 kPa | General tensile requirement | 7–9% | 40–60 | COA sufficient | General-purpose; may accept wider GSM tolerance (±5%) |
| Food-Contact Wrapping (Dry Foods) | 35–60 | ISO 2758: 100–200 kPa | Not critical unless handling stress high | 6–8% | 20–35 | FDA/EC compliance statement + migration test results + COA | Low Cobb essential; requires virgin fiber and certified food-safe sizing; surface strength (pick test) if printing |
| PE/VCI Lamination Substrate | 40–70 | TAPPI T 403: 120–200 kPa | Not critical | 5–7% | 25–45 | COA + surface energy/corona treatment data | Lower moisture aids lamination adhesion; surface prep critical |
| Paper Tubes & Cores (Liner) | 100–180 | ISO 2758: 300–500 kPa | High tensile MD per ISO 1924-2; ring compression critical | 6–8% | 30–45 asneeded | COA + ring crush data | High tensile supports winding stresses; moisture control prevents ovality/creep under load |
| Gypsum Liner / Plasterboard Facing | 150–250 | ISO 2758: 200–400 kPa | Tensile for handling; confirm face and back if different | 7–9% | Varies by bonding requirement | COA + bonding compatibility statement | Surface and backside may require different Cobb/sizing; confirm both with gypsum system |
| Medical Pouches (Paper Side) | 50–80 | ISO 2758: 150–300 kPa | Tensile and tear for peel integrity | 6–8% | 25–40 | COA + sterilization compatibility + microbial barrier validation | Specs driven by validation and regulatory frameworks; treat paper spec as part of system qualification |
How to read this matrix: Each row represents a distinct end-use application with its typical property requirements. The “Evidence to Request” column specifies what documentation buyers should require and suppliers should prepare. COA (Certificate of Analysis) should include test results with method identification, test date, and lot traceability. Test certificate validity of 7–14 days from test date to delivery represents standard practice for bulk orders, though some buyers extend this to 30 days for trial orders where lead time exceeds production scheduling flexibility.
The matrix uses illustrative property bands based on common industry specifications. Actual values should be determined through collaboration between buyer processing requirements and supplier capability data. Specifications near the low end of each range typically indicate cost optimization, while specifications near the high end indicate performance prioritization or demanding end-use conditions.
How to Use the Matrix in RFQs and Buyer–Supplier Conversations
Copy property bands directly from the matrix into RFQ specification fields. Instead of requesting “kraft liner suitable for food packaging,” write: “Kraft linerboard, virgin fiber, 150 GSM ±3%, burst minimum 400 kPa per ISO 2758, tensile index MD ≥50 N·m/g per ISO 1924-2, moisture 7–9% per ISO 287, Cobb maximum 35 g/m² per ISO 535, sampling per ISO 186. COA required showing all test methods and results.”
This precision eliminates ambiguity. Suppliers quote against identical targets and provide evidence tied to the specified methods. RFQ data packs that name ISO/TAPPI methods and attach dated evidence turn receiving from investigation into verification—the QA team compares delivered properties against the test certificate rather than conducting full qualification from scratch.
Request evidence recency aligned with order volume and risk. For ongoing supply contracts, require test certificates dated within 7 days of production. For spot purchases or initial qualification, certificates within 30 days may suffice. For high-value or food-contact applications, some buyers require the supplier to conduct witnessed testing, where the buyer’s representative observes the sampling and testing process at the supplier’s facility or third-party lab.
Three Common Buyer Scenarios
Scenario 1: “The price looks attractive, but will it survive freight and handling?”
Start with the application row in the matrix. For corrugated liners or sack kraft, emphasize burst and tensile properties that correlate with shipping durability. Lock in moisture and Cobb specifications so the paper behaves consistently across different storage and transit conditions, particularly in humid corridors. If price pressure pushes toward recycled content, compensate by increasing basis weight or targeting higher property indices to maintain performance.
Scenario 2: “Specifications differ across suppliers—quotes aren’t comparable.”
Force comparability by requiring method-named specifications in the RFQ: ISO or TAPPI test references, target ranges with tolerances, and COAs showing actual test results. When a supplier proposes alternate test methods, require documentation showing equivalence or cross-reference data between methods. This standardization reveals which suppliers genuinely meet requirements versus those hedging with convenient interpretations.
Scenario 3: “Trial runs succeeded, but production batches failed later.”
Add sampling requirements (ISO 186) and moisture testing (ISO 287) to both RFQ specifications and incoming QC protocols, not just strength properties. Stability over time often depends on moisture control and proper storage rather than headline burst or tensile numbers. Specify acceptable moisture ranges and require suppliers to demonstrate consistent moisture control across production lots.
Suppliers benefit from the same clarity. When a buyer specifies exact property bands and test methods, the supplier can check internal capability data, confirm feasibility, and quote accurately. Kraft paper manufacturers with documented capability matrices showing their typical GSM ranges, burst performance by fiber type, and moisture control limits can respond faster and more accurately than competitors guessing at requirements.
Both parties should document assumptions. If the matrix suggests 7–9% moisture but the buyer’s converting equipment requires 6–8%, note this in the RFQ. If a supplier’s typical production runs 8–10% moisture and they’ll need to adjust process settings to meet 6–8%, flag this during quoting to manage lead time and pricing expectations. These conversations prevent post-award disputes when written specifications meet but operational reality diverges from assumptions.
Edge Cases and Trade-Offs
The matrix represents typical applications, but several factors create edge cases requiring adjusted specifications.
Moisture versus Cobb trade-offs appear when balancing dimensional stability against processing requirements. Food-contact wrapping needs low Cobb (under 30 g/m²) to prevent grease penetration, but very low moisture (below 6%) can make the paper too brittle for tight folds. The solution involves surface sizing to reduce Cobb without requiring extremely low moisture, keeping the paper flexible enough for commercial wrapping equipment while maintaining the barrier properties needed for direct food contact.
Recycled versus virgin strength expectations shift the burst and tensile targets. Recycled fiber generally delivers 15–25% lower burst strength than virgin kraft at equivalent GSM due to shorter fiber length and reduced bonding. Rather than rejecting recycled content, some buyers adjust specifications: a virgin linerboard spec might call for 140 GSM at 400 kPa burst, while the recycled equivalent targets 160 GSM at 380 kPa—using slightly heavier basis weight to compensate for the inherent strength difference. This works when cost savings from recycled content exceed the material weight penalty.
Lamination and coating effects alter both Cobb and processing behavior. Polyethylene lamination essentially eliminates moisture transmission, making the base paper’s Cobb value less critical. However, PE lamination requires lower base-paper moisture (5–7%) during the lamination process to prevent blistering. Similarly, heavy surface sizing can reduce Cobb from 55 g/m² down to 30 g/m², but it adds 3–5 GSM of coating weight that must be factored into total basis weight and cost calculations.
Climate and storage conditions influence moisture equilibrium. Paper produced and tested in Northern Europe at 50% relative humidity may arrive in Southeast Asia at 80% humidity and equilibrate to 10–11% moisture, causing dimensional changes or processing issues. Specifications for tropical climates sometimes set tighter Cobb maximums (under 40 g/m²) or require moisture barrier packaging for the entire shipment. Buyers in high-humidity regions should verify that test certificates reflect realistic storage conditions rather than ideal laboratory environments.
These edge cases reinforce the matrix’s role as a starting framework, not a rigid rulebook. The property bands represent common industry practice, but specific applications may require adjustments based on processing equipment capabilities, climate factors, or regulatory requirements beyond general food-contact frameworks.
Checklist: From Spec to Successful Use
Use this sequence to move from matrix reference to operational procurement:
1. Select the application row that matches your end use. If your application spans multiple rows (for example, a sack that also requires food contact), combine the most restrictive requirements from each relevant row.
2. Copy property bands into RFQ fields with tolerances explicitly stated. Write “GSM 100 ±3%” rather than “approximately 100 GSM” to establish measurable acceptance criteria.
3. Name the test method for each property. Specify “burst per ISO 2758” or “tensile index MD per ISO 1924-2” rather than generic “burst strength” or “tensile” to ensure suppliers test against the method you’ll use for acceptance.
4. Define evidence requirements including certificate age. Request “COA dated within 14 days of production, showing results for GSM (ISO 536), burst (ISO 2758), tensile MD/CD (ISO 1924-2), moisture (ISO 287), and Cobb (ISO 535). Sampling per ISO 186.”
5. Add acceptance clauses to the purchase contract. Language like “delivered product shall conform to specifications within stated tolerances as verified by buyer’s testing per the same ISO/TAPPI methods” creates enforceable quality gates.
6. Specify retention sample procedures. Require the supplier to seal and label 2–3 rolls or sheets from each production lot, holding them for 90 days post-delivery for reference in case of quality disputes.
7. Establish corrective action protocols for off-spec deliveries. Define what constitutes a minor deviation requiring documentation versus a major deviation requiring replacement, and specify response timelines for each scenario.
8. Link specifications to landed cost analysis. Properties affect usable yield—a lower-burst paper may generate 2–3% more breakage waste, effectively increasing cost per finished unit even if the quoted price appeared competitive. Normalize quotes to total cost-to-door including freight, duties, and yield factors before selection.
9. Verify supplier capability before awarding. Request evidence that the manufacturer’s process capability can consistently deliver the specified property bands, not just that they once produced a conforming lot. Process performance indices above 1.33 indicate reliable capability.
10. Plan periodic audits for ongoing supply relationships. Even established suppliers experience quality drift due to raw material changes, equipment wear, or process adjustments. Quarterly or semi-annual reviews of test certificates and occasional witnessed testing maintain specification integrity over multi-year contracts.
Ready to source kraft paper suppliers with verified capabilities? Explore kraft paper manufacturers and connect directly with mills and exporters. For immediate sourcing needs, submit your RFQ with complete specifications to receive comparable quotes from multiple verified suppliers.
Further Learning
This matrix provides the foundation for specification-driven kraft paper procurement. Additional resources address related topics:
Sample testing protocols to request during pre-qualification explain which tests to require before approving new suppliers and how to interpret laboratory reports.
How freight scenarios flip supplier rankings demonstrates why landed cost comparison requires normalizing quotes across different Incoterms before applying property-based selection.
Remote versus on-site supplier audits clarifies when process verification requires physical presence versus when method-aligned test reports provide sufficient assurance.
Contract clauses that protect against off-spec deliveries offers enforceable language for specifications, testing protocols, remedies, and audit rights that reduce disputes when quality issues emerge.
For fundamentals on kraft paper test methods, TAPPI provides comprehensive overviews of physical property testing standards.
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