Packaging Materials Guide: Corrugated Flutes, Paperboard Points and Rigid Board

Why material is the decision you can't fix later

You can change a color, move a logo or add a foil to a box in the next reorder. Changing the material often means changing the dieline, the insert, the price, the shipping performance and the look all at once. Material choice decides whether products arrive intact, how colors print, how the box feels in the hand, how much it costs and whether customers can recycle it.

This guide explains the three main families of packaging board (corrugated, paperboard and rigid greyboard), how each is made, how strength and thickness are specified, and how to pick the right grade for your product.

Part 1: Corrugated board

How corrugated is made

Corrugated board is made on a corrugator. A roll of paper called the medium is heated, steamed and pressed between fluted rollers to form a wave pattern (the flutes). Starch adhesive is applied to the flute tips, and flat papers called liners are bonded on one or both sides. The resulting board is extremely stiff for its weight because the flutes act like a row of arches.

Flute sizes

Liners

• Kraft liner: unbleached and brown, very strong.
• White top / bleached liner: bright surface for printing.
• Recycled (test) liners: economical, slightly lower strength per weight.

Strength: ECT, Mullen and BCT

Three numbers come up repeatedly:

• ECT (Edge Crush Test): the force in pounds per inch the board withstands on its edge. Predicts stacking strength. Common grades: 32, 44, 48, 61 ECT.
• Mullen (burst): the pressure needed to puncture the board face, in psi. Common grades: 200#, 275#, 350#.
• BCT (Box Compression Test): the load a finished box can carry before collapsing. It depends on ECT, board thickness and box size.

The McKee formula estimates box compression from ECT, caliper and box perimeter:

Rule of thumb: BCT ≈ 5.87 × ECT × √(caliper × perimeter). A larger perimeter and thicker board increase compression strength.

Try it with our Box Strength Calculator.

Real-world strength drops with humidity, time under load, poor pallet patterns and overhang. In humid warehouses, corrugated can lose a large share of its stacking strength, so engineers apply safety factors of 3 to 5 when designing for long storage.

Choosing corrugated

Part 2: Paperboard

What paperboard is

Paperboard is thick paper, usually more than 0.010 in (10 points) thick, used for folding cartons. It may be single-ply or multi-ply, and it is often clay-coated on the printing side for a smooth surface.

Thickness in points

Paperboard thickness (caliper) is measured in points: 1 pt = 0.001 inch. To convert between points, GSM and pound weights, use our paper weight chart. Common calipers are 14, 16, 18, 20 and 24pt. 18pt is the most common for retail cartons.

The main grades

Read the full profiles: SBS, kraft, recycled.

Grain direction and folding

Paperboard has a grain: the direction most fibers run. Board folds more easily and cleanly parallel to the grain, and is stiffer across it. Carton makers orient the grain so the main panels are stiff and the folds are clean. If you see cracking on folds, grain direction, board grade, moisture or dark ink coverage may be the cause.

Coated vs. uncoated

• Coated (C1S/C2S): smoother, brighter, better for photography and fine detail, and for laminations and spot UV
• Uncoated: natural, tactile, absorbs ink (colors look softer), embosses beautifully

Part 3: Rigid greyboard

Rigid boxes use greyboard (chipboard), a dense recycled board typically 1–3 mm thick, wrapped in printed or specialty paper. It is not creased and folded like a carton; it is cut, its corners are grooved and stayed, and it is wrapped.

See rigid chipboard.

Part 4: Flexible materials

Pouches and bags use laminated films (PET, PE, metallized films, foil) and papers. Each layer does a job: print surface, barrier and sealant. Barrier needs depend on the product's sensitivity to oxygen, moisture and light, and on the target shelf life. See stand-up pouches.

Matching material to product

Material and sustainability

• Corrugated typically contains a high share of recycled fiber and is widely recycled.
• Paperboard cartons are widely recyclable; CRB is made from recycled fiber.
• Rigid boxes are often reused; recyclable once non-paper parts are removed.
• Flexible films save weight but are mostly not curbside recyclable; mono-material options can be recycled through store drop-off where accepted.

Right-sizing often reduces impact more than switching materials. Read our sustainable packaging guide.

Specification checklist

When you request a quote, specify:

• Material family (corrugated, paperboard, rigid, flexible)
• Grade (for example E-flute 32 ECT white; 18pt SBS C1S; 2 mm greyboard)
• Liner or surface (kraft, white, coated, uncoated)
• Inside print or not
• Coating or lamination
• Any food-contact or barrier requirements

How to choose a material: a decision path

Most material decisions come down to five questions, answered in order:

1. Does the package travel through a parcel network on its own? If yes, start with corrugated. If it sits on a shelf or inside another box, paperboard is usually enough.
2. How heavy and fragile is the product? Heavier products need stronger corrugated grades or thicker paperboard; fragile products need inserts more than heavier board.
3. Does it need a barrier? Food, coffee, powders and products sensitive to moisture or oxygen may need a flexible laminate, a liner or a coated board.
4. What should it look and feel like? White board for bright, accurate color; kraft for a natural look; rigid board for a keepsake.
5. What are your sustainability goals? Paper-based, mono-material packaging is easiest to recycle in the US; recycled content and certified fiber support specific claims.

Material properties side by side

Material and print interactions

Materials change how print looks:

• White corrugated (white top) gives bright color; fine detail depends on flute size.
• Kraft corrugated darkens and warms colors; best with one or two dark inks or white ink.
• SBS reproduces color and detail most accurately among paperboards.
• CUK prints like white board on its coated face with kraft strength behind.
• CRB prints very well on its coated face; the back is grey.
• Rigid box wraps are printed on paper before wrapping, so any paper printing process applies.
• Flexible films are usually reverse-printed with rich, glossy color.

See the printing guide for process details.

Material and finish compatibility

Material costs in context

Board is only one part of packaging cost. At low quantities, setup, printing and conversion often matter more than the material itself, so switching to a cheaper board may save less than expected. At high quantities, material becomes a larger share of the price, and choices like caliper and grade make a bigger difference. Our pricing model shows these effects directly: compare materials for your size and quantity on any product page or in the Packaging Cost Calculator.

Material mistakes to avoid

1. Using paperboard for parcel shipping without an outer box.
2. Over-specifying corrugated (double-wall for light products).
3. Under-specifying for storage in humid warehouses.
4. Choosing kraft for bright brand colors without white ink.
5. Putting food against non-food-contact board.
6. Mixing materials that customers cannot separate for recycling.

Material glossary

• Basis weight: weight of paper per thousand square feet (lb/MSF).
• Caliper: thickness of board, in points (pt) or millimeters.
• CRB: coated recycled board.
• CUK: coated unbleached kraft.
• ECT: edge crush test, a measure of corrugated stacking strength.
• Flute: the wavy middle layer of corrugated board; sizes A, B, C, E, F.
• Greyboard: dense recycled board used in rigid boxes.
• Linerboard: the flat paper facings of corrugated board.
• Medium: the fluted paper in corrugated board.
• SBS: solid bleached sulfate paperboard.
• Laminate: layers of film bonded together, used in pouches.
• Barrier: resistance to oxygen, moisture, light and aroma.

See the full glossary.

Materials by industry

How paperboard and corrugated are made

Most packaging materials begin as wood fiber. In a pulp mill, wood chips are cooked to separate fibers (the kraft process for strong fibers) or ground mechanically. Fibers may be bleached for white board or left unbleached for kraft. Recovered paper is repulped and cleaned for recycled grades.

On a board machine, a dilute fiber suspension is spread onto moving screens, drained, pressed and dried into a continuous web. Multi-ply machines form several layers with different fibers, for example cleaner fibers on the surface and recovered fibers in the middle. Coatings of minerals and binders are applied for printing surfaces and polished by calendering.

Corrugated board is made on a corrugator, which combines rolls of linerboard and medium: the medium is heated and fluted between corrugating rolls, starch adhesive is applied to the flute tips, and liners are bonded on. The board is cut into sheets for converting into boxes.

Understanding these steps explains differences between grades: why SBS is white throughout, why CRB has a grey back, why kraft is strong and brown, and why corrugated strength depends on the papers and flute chosen.

Reading a board specification

A supplier's specification for board might include:

You do not need every detail to order packaging, but asking suppliers to state grade, caliper or flute, and strength makes quotes comparable.

Three material decisions, worked through

A candle brand shipping glass jars. The candles travel through parcel networks, are fragile and moderately heavy. Material: E-flute corrugated mailer (32 ECT) with a corrugated insert, white outside for full-color print and kraft inside. Inside each mailer, the retail carton is 18pt kraft for a natural look.

A snack brand entering grocery. The product ships in cases to stores and sits on shelves; it needs a moisture barrier. Material: CRB carton for economy and printability with a sealed inner bag; corrugated shipper cases.

A jewelry brand's gift box. The box is kept as storage and must feel luxurious. Material: 1.5 mm greyboard rigid box wrapped in soft-touch printed paper, with a paper-wrapped insert; shipped inside a small corrugated mailer.

Material availability and lead times

Most common boards (E-flute and C-flute corrugated, SBS, kraft and CRB in standard calipers) are readily available. Specialty materials can take longer: certified fiber in specific grades, unusual calipers, colored-through boards, metallized boards, specialty wrap papers for rigid boxes and high-barrier pouch laminates. If your design depends on a specialty material, ask about availability and lead time when you request a quote, and consider a standard alternative as a backup.

Materials and printing costs together

A common mistake is choosing a material and then discovering that the print or finish you want is difficult or expensive on it. Decide material, print and finish together: for example, bright photographic print suggests SBS or white-top corrugated; a natural kraft look suggests one or two dark inks and foil; a luxury tactile experience suggests rigid wraps with soft-touch and emboss. The finishes guide and printing guide explain these combinations.

Matching material to storage and climate

Where packaging is stored and shipped affects material choice:

If your packaging will face unusual conditions, tell us when requesting a quote.

Frequently confused material terms

Cardboard vs. paperboard vs. corrugated. In everyday speech, cardboard means any stiff paper material. In packaging, paperboard means solid board used for cartons (like cereal boxes), and corrugated means fluted board used for shipping boxes.

Chipboard vs. greyboard. Often used interchangeably for dense recycled board. In rigid boxes, greyboard is the thick structural board inside the wrap.

Kraft vs. brown. Kraft refers to the kraft pulping process and the strong unbleached fiber it produces. Not all brown board is virgin kraft; recycled board can also be brown.

Recycled vs. recyclable. Recycled describes what a material is made from; recyclable describes what can happen to it after use.

Coated vs. laminated. Coatings are liquids applied to the surface; laminations are films bonded to it.

Film vs. foil. In packaging, film usually means plastic film (PET, PP, PE); foil can mean aluminum foil in laminates or the metallic layer applied in foil stamping.

Using the right terms with suppliers avoids quotes for the wrong material.

Testing a new material

Before switching materials for an existing product, test:

1. Print samples to check color and detail.
2. Structural samples to check fit, stiffness and fold quality.
3. Shipping tests if the package travels by parcel.
4. Storage tests in your warehouse conditions.
5. Customer reactions if the look and feel change noticeably.

Material changes can affect everything from color to recyclability claims, so document results and update specifications.

Choosing board thickness: worked examples

A 1 oz serum bottle in a carton. Light product, small panels: 16–18pt SBS is enough. Thicker board would make folds harder and add cost without benefit.

An 8 oz glass candle in a carton. Heavier and fragile: 20pt board with an auto-lock bottom and a ring insert, shipped inside a mailer.

A 3 lb gift set shipped to customers. Too heavy for paperboard alone: E-flute or B-flute mailer with inserts.

A 25 lb wholesale case stacked on pallets. C-flute 44 ECT or double-wall, depending on stacking height and storage time; check with the Box Strength Calculator.

A large rigid presentation box. 2.5 mm greyboard to keep walls flat and corners crisp.

The pattern: match thickness to weight, panel size and handling, and solve fragility with inserts rather than ever-thicker board.

Material and brand positioning

Materials communicate before customers read a word:

Choose the material that supports your positioning, then make sure the claims you make about it are accurate.

Material FAQ, extended

Is E-flute strong enough for shipping? Yes, for most products under about 10 lb in a right-sized box, especially mailers.

What is the difference between B-flute and C-flute? C-flute is thicker and offers more cushioning and stacking strength; B-flute is thinner with better crush resistance and print surface.

What paperboard is best for food? SBS with suitable coatings for direct contact; CRB with an inner bag for indirect contact.

Why is rigid board grey? It is usually made from recycled fiber; the wrap paper provides the look.

Material developments to watch

Packaging materials keep evolving. Developments that brands are watching include:

• Paper-based barrier coatings that let paperboard and paper replace some plastic for food and moisture-sensitive products.
• Improved molded fiber, including smoother "thermoformed" pulp that looks premium enough for cosmetics and electronics.
• Mono-material flexible films designed for recycling streams where they are accepted.
• Higher-performance recycled boards that close the gap with virgin grades.
• Digital printing on corrugated that makes short runs of full-color shipping boxes economical.

When considering a new material, ask for samples, test performance with your product, and check that any environmental claim you plan to make is supported for your specific material and market.

Materials and the customer's hands

Customers judge materials by touch in a fraction of a second. Thin, flexible board feels cheap; stiff board with crisp folds feels considered. Uncoated kraft feels natural and slightly rough; coated SBS feels smooth and clean; soft-touch laminated board feels velvety; rigid board feels solid and heavy. Corrugated feels practical and protective. When you choose a material, hold samples in your hand alongside your product and ask whether the feel matches the price and personality of what is inside. Our sample kit includes board and finish swatches for exactly this purpose.

A material decision record

Keep a short record of each packaging material decision: the product, the chosen material and grade, why you chose it, alternatives considered, test results and supplier. When you reorder, change suppliers or add new products, this record saves time and prevents accidental downgrades, such as a lighter board slipping into a reorder without anyone noticing.

Materials checklist before ordering

• [ ] Shipping method decided (parcel, retail, freight)
• [ ] Product weight and fragility known
• [ ] Barrier needs identified
• [ ] Look and feel chosen (white, kraft, rigid, film)
• [ ] Print and finish compatibility checked
• [ ] Storage conditions considered
• [ ] Recyclability and claims reviewed
• [ ] Samples requested where uncertain

Materials and costs over the life of a product

A product's packaging often changes over its life. At launch, flexibility matters more than unit price: short digital runs on standard boards let you adjust quickly. As sales grow, you can optimize: lighter grades where tests show they perform, recycled boards for high-volume items, and specialty materials only where they add value. When a product matures, standardizing materials across the line simplifies purchasing and reduces cost. Plan material choices with this life cycle in mind rather than choosing the "perfect" material on day one.

Summary: what to remember

• Use corrugated for shipping and paperboard for shelves.
• Choose board grade by weight, stacking and storage conditions.
• Choose white board for bright color, kraft for a natural look.
• Use rigid board for keepsake and gift packaging.
• Use flexible films when barrier and light weight matter.
• Solve fragility with inserts, not just thicker board.
• Keep packaging in one material family where possible.
• Test samples before switching materials.

Common mistakes to avoid

Choosing the thickest board available. Thicker board costs more, weighs more and can make folds crack, without solving movement inside the box. Fix fragility with a good insert and right-sizing first.

Using paperboard for shipping. Folding carton board is strong for its weight on a shelf but not built for parcel drops and stacking. Shipping packaging needs corrugated.

Expecting white-board color on kraft. Brown kraft absorbs ink and darkens colors. Design for kraft deliberately, or use a white-top or white board when colors must be bright.

Ignoring humidity and cold storage. Paper-based materials lose strength in damp conditions. Products stored in fridges, freezers or humid warehouses need coatings, higher grades or different materials.

Mixing materials unnecessarily. A box with plastic windows, foam inserts and laminations is harder to recycle. Keep components in one material family where possible.

Switching material without testing. A new board, even with similar specs, can behave differently. Test samples with real products and real shipping before changing a production order.

If you are still unsure which board is which, read corrugated vs cardboard vs paperboard, a plain-English explainer of the three boards people call cardboard.

Related products & pages

MaterialsCorrugated CardboardFluted board for mailers and shippers: E, B, C and double-wall grades from 32 to 48 ECT. MaterialsSBS PaperboardBright white premium paperboard (14–24pt) for cosmetics, pharma and retail cartons. MaterialsKraft PaperboardNatural brown, unbleached board with a handmade, eco-forward look. MaterialsRigid ChipboardThick 1.2–3 mm greyboard wrapped in paper for luxury setup boxes.