Paper Grades Explained: Kraftliner, Testliner, Fluting, Duplex Board, and More

Every transaction in paper trading starts with the same question: what grade? Whether you are a procurement manager sourcing containerboard for a corrugated box plant, a converter looking for coated board for retail packaging, or a mill trying to move surplus inventory, the language of paper grades is the foundation of every deal.

This guide covers the major grade families traded in European and global surplus markets, their specifications, typical GSM ranges, and practical advice for buying surplus paper at a discount.

The Basic Unit: GSM

Paper weight is measured in grams per square meter (GSM), sometimes written as g/m². This is the single most important number in any paper specification. It tells you the weight — and by extension the thickness, stiffness, and suitability — of the paper for a given application.

A few reference points:

• Standard copy paper: 80 GSM
• Lightweight fluting medium: 90 GSM
• Standard kraftliner: 125–175 GSM
• Corrugated box liner: 150–300 GSM
• Folding boxboard: 200–450 GSM
• Tissue: 15–25 GSM

GSM is always the first number in any surplus listing. When a buyer searches for "testliner 150 GSM," they are specifying both the grade family and the weight. Getting comfortable with GSM ranges across different grades is the fastest way to become literate in paper trading.

It is worth noting that GSM measures weight per area, not thickness directly. Two papers with identical GSM can have different caliper (thickness in microns) depending on how they were manufactured. Bulk — the ratio of caliper to GSM — matters particularly in packaging grades where stiffness is critical.

The Main Grade Families

Kraft Paper

Kraft paper is made from chemical wood pulp using the kraft process (from the German word for "strength"). The result is a strong, brown, durable paper used for bags, sacks, wrapping, and as liner material in corrugated packaging.

Key characteristics:
- Made from virgin wood fiber (softwood pulp, typically pine or spruce)
- Natural brown color, though bleached white kraft also exists
- High tear strength and burst strength relative to weight
- GSM range: 40–120 GSM for sack kraft, 125–440 GSM for kraftliner

Common sub-grades:
- Sack kraft (40–120 GSM): Used for industrial bags — cement, chemicals, flour, animal feed. Must survive filling, transport, and stacking.
- MG kraft (Machine Glazed): One side is glossy, used for wrapping and carrier bags.
- Bleached kraft: White kraft used in premium packaging where appearance matters.

Kraft is a staple surplus grade because it is produced in enormous volumes across Europe and South America. Mills running kraftliner lines frequently generate remnants and changeover rolls that are fully functional but do not match a specific customer order.

Containerboard: Linerboard and Fluting

Containerboard is the umbrella term for the papers used to make corrugated boxes — the brown cardboard boxes that ship virtually everything in the global economy. It is the largest and fastest-growing paper category, driven by e-commerce and the shift from plastic to paper-based packaging.

Containerboard has two components:

Linerboard — the flat outer and inner layers of a corrugated box. This is the surface you see and print on.

Fluting medium — the wavy (corrugated) inner layer that provides structural rigidity. This is the accordion-like layer between the two liners.

Kraftliner

Kraftliner is the premium grade of linerboard, made predominantly from virgin kraft pulp. It delivers superior strength, consistent quality, and a clean surface for printing.

• GSM range: 125–440 GSM (most common: 135, 150, 175, 200, 250, 300)
• Key properties: High ring crush (RCT), high burst, good printability
• Producers: Mondi, Smurfit WestRock, Stora Enso, International Paper, Suzano
• Surplus availability: High — large production volumes mean consistent surplus generation

Testliner

Testliner is linerboard made partly or entirely from recycled fiber. It is cheaper than kraftliner and used where maximum virgin-fiber strength is not required.

• GSM range: 100–350 GSM (most common: 115, 125, 140, 150, 175, 200)
• Key properties: Lower strength than kraftliner at equivalent GSM, varies by recycled content
• Grading: Testliner 2 (TL2, brown, from 100% recycled fiber) and Testliner 3 (TL3, lower quality) are the most common. White-top testliner has a white coated surface for printing.
• Surplus availability: Very high — recycled containerboard mills run at enormous scale

Buyers who can accept testliner instead of kraftliner for their application can achieve significant cost savings, especially in the surplus market where testliner discounts stack on top of the already lower base price.

Fluting Medium

Fluting is the corrugated layer that gives a cardboard box its strength-to-weight ratio. When you look at the edge of a corrugated box and see the wavy pattern, that is the fluting.

• GSM range: 80–200 GSM (most common: 90, 105, 112, 115, 127, 150)
• Key properties: Good CMT (Corrugating Medium Test), SCT (Short-span Compression Test), stiffness
• Types: Semi-chemical fluting (from virgin fiber, highest quality), recycled (wellenstoff), and lightweight fluting
• Surplus availability: High — fluting lines produce significant remnant and changeover rolls

Containerboard Surplus: What to Know

Containerboard accounts for the largest share of surplus paper traded globally. The reasons are structural: these grades are produced in massive volumes on machines that run 24/7, and every order requires precise width slitting from large master rolls. The leftover widths, changeover rolls during grade transitions, and overstock from cancelled orders all become surplus.

For buyers, surplus containerboard is often identical in quality to prime material. A remnant roll of 175 GSM kraftliner has the same ring crush, burst, and moisture properties as the roll that filled the original order — it simply was not the right width for that particular customer. This makes containerboard surplus one of the most attractive categories for cost-conscious converters.

Duplex Board and Folding Boxboard

Duplex board (also called coated duplex board or GD — greyback duplex) is a multi-layer board with a white coated top surface and a grey or brown back made from recycled fiber. It is the workhorse of retail packaging: cereal boxes, pharmaceutical cartons, consumer goods packaging.

• GSM range: 200–500 GSM (most common: 230, 250, 300, 350, 400, 450)
• Key properties: Good printability on the coated surface, adequate stiffness, lower cost than solid bleached board
• Sub-grades:
• GD2: White-coated front, grey back, most common grade
• GD3: Lower quality coating, sometimes mottled back
• GT (greyback triplex): Three-layer board with middle layer from recycled fiber
• Surplus availability: Moderate — produced in significant volumes but fewer mills specialize in board grades

Folding boxboard (FBB) is the premium alternative — made from virgin fiber with a white back. Used for cosmetics, luxury goods, and food-contact packaging. FBB surplus commands lower discounts than GD because demand is consistently high.

Uncoated Woodfree (UWF) / Freesheet

Uncoated woodfree paper is what most people think of as "office paper" or "copy paper." It is white, smooth, takes ink well, and is used for printing, stationery, books, and documents.

• GSM range: 60–120 GSM (most common: 70, 75, 80, 90, 100, 120)
• Key properties: Brightness (measured in ISO %, typically 90–98%), opacity, smoothness, printability
• Declining market: Global UWF demand has been declining for over a decade as digital replaces print. However, production volumes remain large, and surplus is common.
• Surplus availability: High — mills frequently overproduce against orders, and brightness or shade deviations create off-spec inventory

For surplus buyers, UWF is interesting because brightness deviations that make paper "off-spec" for one customer are often perfectly acceptable for another. A buyer who needs 92% brightness paper for exercise books may happily accept a lot that was rejected because it measured 91.5% instead of the ordered 93%.

Coated Paper

Coated paper has a layer of mineral coating (typically kaolin clay and calcium carbonate) applied to one or both surfaces. This creates a smooth, glossy or matte finish ideal for high-quality printing.

• GSM range: 70–350 GSM depending on sub-grade
• Sub-grades:
• LWC (Lightweight Coated): 50–80 GSM, used for catalogues, magazine inserts, advertising flyers
• MWC (Medium Weight Coated): 80–130 GSM, used for magazines, brochures, annual reports
• Art paper / C2S (Coated Two Sides): 100–350 GSM, used for premium brochures, art books, high-end packaging
• C1S (Coated One Side): Used for labels and some packaging applications
• Surplus availability: Moderate — coated paper production is declining in Europe, but remaining mills still generate surplus from specification mismatches

Tissue

Tissue is in a category of its own. It is lightweight (15–25 GSM), soft, highly absorbent, and manufactured on entirely different machines (Yankee dryers) than other paper grades. Tissue includes toilet paper, facial tissue, kitchen towels, napkins, and industrial wipers.

• GSM range: 13–30 GSM for base tissue (before converting)
• Key properties: Softness, absorbency, wet strength (for towels), bulk
• Surplus availability: Limited in traditional surplus channels — tissue mills typically convert in-house or sell parent rolls to dedicated converters. However, parent roll surplus does occur.

Tissue is generally not interchangeable with other grades and requires specialized converting equipment. Surplus tissue parent rolls can be attractive to independent converters who lack their own paper machines.

Specialty Grades

Specialty papers serve niche applications with specific performance requirements that standard grades cannot meet.

• Greaseproof / Baking paper: Resistant to oil and fat penetration, used in food service and baking
• Release paper / Silicone base: Carrier paper for labels, tapes, and composites
• Security paper: Watermarked, with embedded fibers or threads, used for currency, passports, certificates
• Filter paper: Used in automotive, industrial, laboratory, and food filtration
• Thermal paper: Coated with heat-sensitive chemicals for receipt printers
• Label stock: Self-adhesive face paper for labels, available in many finishes
• Decor paper: Printed paper impregnated with resin, used on furniture and flooring surfaces

Specialty grades are harder to trade as surplus because the buyer pool for any given specification is small. However, when a match is found, the margins can be attractive — specialty papers command higher per-ton prices, and surplus discounts of 20-30% on a high-value grade can be substantial in absolute terms.

What Moves Most in Surplus Markets

Not all grades generate equal surplus volumes or trade with equal frequency. The hierarchy follows production volume:

1. Containerboard (kraftliner, testliner, fluting) — the largest category by far. High volumes, standardized specifications, and a deep buyer pool make this the most liquid surplus market.
2. Kraft paper — closely related to containerboard, also high volume and widely traded.
3. Uncoated woodfree (UWF) — large production base generates consistent surplus, though the market is shrinking.
4. Coated paper — declining production means fewer new surplus lots, but existing inventory still needs to move.
5. Board grades (duplex, FBB) — moderate volumes with a solid converter buyer base.
6. Tissue and specialty — the least liquid surplus markets due to specialized requirements and smaller buyer pools.

For a deeper understanding of why surplus exists and how it is created, see our guide on what surplus paper is and how it originates.

How to Read a Surplus Paper Listing

Every surplus listing — whether on a marketplace platform, in a broker email, or on a mill's availability list — contains a standard set of specifications. Here is what to look for:

Brightness matters most for printing grades. Higher percentages mean whiter paper. A brightness difference of 1-2 ISO points may be imperceptible in the finished product but enough to classify the paper as off-spec against the original order.

Opacity matters so text and images do not bleed through to the other side. It is critical for book papers and office grades, less so for packaging.

Width is crucial in surplus because remnant rolls are typically narrower than standard widths. A buyer who can use 950 mm rolls will find more surplus available at better prices than one who requires exactly 1,600 mm.

For details on how surplus types affect pricing, see our guide on how surplus paper is priced.

Paper Grades Reference Table

Practical Tips for Buying Surplus by Grade

Containerboard buyers: This is the deepest surplus market. Flexibility on width is the single biggest lever — if you can accept rolls that are 50–100 mm narrower than your ideal, your available supply (and discount) increases dramatically. Also consider testliner where you currently specify kraftliner. For many corrugated applications, the strength difference at equivalent GSM is negligible.

UWF buyers: Brightness is the most common reason paper becomes off-spec. If your application tolerates a 1-2 point brightness variance, you unlock a much larger pool of surplus at 20-30% discounts. Ask the mill for the actual test certificate — the paper may exceed your minimum requirements even if it failed the original customer's tighter spec.

Board buyers: Duplex board surplus often comes from short runs and cancelled orders. These lots are typically prime quality and fully printable. The discount is driven by urgency (the mill needs warehouse space) rather than any quality issue.

Coated paper buyers: LWC and MWC surplus is increasingly scarce as European mills close or convert to packaging. When available, it moves fast. Build relationships with the remaining producers and be ready to act quickly on surplus notifications.

General advice: Always request a test certificate (COA — Certificate of Analysis) before committing to a surplus purchase. Reputable mills provide this as standard. The certificate confirms actual GSM, brightness, opacity, moisture content, and mechanical properties against the grade specification. A transparent marketplace should make these certificates available alongside every listing.

Conclusion

Understanding paper grades is not optional in surplus trading — it is the prerequisite. The difference between kraftliner and testliner, between a 150 GSM and a 175 GSM fluting, between a GD2 and an FBB, determines whether a surplus lot is worth pursuing and at what price.

The surplus market rewards buyers who are knowledgeable and flexible. Knowing that a testliner 2 at 140 GSM can substitute for a kraftliner at 125 GSM in certain applications, or that a brightness deviation of 1.5% on UWF is irrelevant for exercise book production, creates opportunities that less informed buyers miss entirely.

For an overview of the different types of surplus and how they originate in the production process, read What Is Surplus Paper?. To understand how grade and surplus type interact to determine pricing, see How Surplus Paper Is Priced.