Liners, mediums, and the air between them.
Corrugated is a structural sandwich: flat liners carrying tension and compression, a fluted medium holding them apart. Almost everything about a box's performance comes from how many of those layers it has and how tall the waves are.
Spec a construction
Tell us the load, the stack height and the handling — we will spec the wall.
Two liners, one medium. Add a second medium and third liner and you have double wall; a third medium and fourth liner gives triple.
What each one is genuinely for.
| Build | Construction | Strength rating | Stacking | In practice |
|---|---|---|---|---|
| Single wall | One fluted medium between two liners | 32 – 44 ECT | Up to 65 lb | The everyday shipper. Lightest, cheapest, most recyclable. |
| Double wall | Two fluted mediums, three liners | 48 – 61 ECT | Up to 120 lb | The workhorse of reuse — survives six to twelve trips with care. |
| Triple wall | Three fluted mediums, four liners | 67 – 82 ECT / 1,100 lb test | 1,200 – 2,400 lb | Gaylord territory. Replaces wooden crates on many lanes. |
| Triple wall + corner posts | Triple wall with laminated vertical posts | Beyond standard ECT scale | 3,000 lb + | Where the alternative is steel. Rare, expensive, very long-lived. |
Double wall is not one thing.
A BC double wall and an EB double wall behave completely differently. The combination matters as much as the layer count.
| Flute | Approx. thickness | Density | Character |
|---|---|---|---|
| A | ≈ 3/16" | 33 flutes/ft | Highest cushioning and stacking strength; bulky, poor print. |
| B | ≈ 1/8" | 47 flutes/ft | Crush resistant, great for canned goods and printing. |
| C | ≈ 11/64" | 39 flutes/ft | The default compromise — most RSC shippers in the US. |
| E | ≈ 1/16" | 90 flutes/ft | Thin, crisp print surface; retail and subscription boxes. |
| F | ≈ 1/32" | 128 flutes/ft | Micro-flute for small, premium primary packaging. |
| N | ≈ 1/64" | 200+ flutes/ft | Nano-flute; folding-carton replacement, rarely seen in reuse. |
| BC | ≈ 5/16" | Double wall | B + C combined — the common double-wall build. |
| EB | ≈ 3/16" | Double wall | Thin, stiff, excellent print. Retail rather than logistics. |
| AC | ≈ 23/64" | Double wall | Maximum cushioning double wall; bulky and uncommon. |
| BCA | ≈ 1/2" | Triple wall | Gaylord territory. 1,100 lb test and crate replacement. |
BC double wall
The common build. B flute inside for crush resistance, C outside for cushioning and thickness. Most used double-wall shippers you will see are BC.
EB double wall
Thin and stiff with an excellent print surface. Retail and subscription packaging rather than bulk logistics.
AAC / BCC triple
Gaylord territory. Maximum stacking strength, used where the alternative is a wooden crate.
| Mullen (burst) | ECT (stacking) | Wall | Max gross weight, typical |
|---|---|---|---|
| 200 lb | 32 ECT | Single | 65 lb |
| 275 lb | 44 ECT | Single | 95 lb |
| 275 lb | 48 ECT | Double | 120 lb |
| 350 lb | 51 ECT | Double | 180 lb |
| 500 lb | 61 ECT | Double | 260 lb |
| 700 lb | 71 ECT | Triple | 600 lb |
| 1,100 lb | 82 ECT | Triple | 2,400 lb static |
Mullen measures puncture
A diaphragm is pushed through the board until it bursts, reported in psi. Tells you about drops, corner impacts and dragging across a dock plate. Designed for rough single-trip handling.
ECT measures stacking
A strip of board is crushed on its end, reported in pounds per linear inch. Predicts how high a pallet stacks before the bottom box fails. In a palletised chain, this is nearly always the number that matters.
Three ways people buy strength they cannot use.
Over-specification is as common as under-specification and costs more money, because you pay for it on every single unit.
Stepping up the wall when the flute was the problem
If boxes are failing from crush on a printed face, B flute solves it for less than double wall does.
Buying triple wall for a 400 lb load
A 61 ECT double wall handles it comfortably. Triple wall costs more, weighs more to ship, and adds nothing.
Specifying Mullen on a palletised lane
You are paying for puncture resistance and then measuring a stacking failure. Specify the test that matches the failure mode you actually see.
Mullen and ECT, side by side.
Two tests measuring two different failure modes. The equivalences below exist because carriers historically specified Mullen — treat them as conversational rather than contractual, and pick the test that matches how your boxes actually fail.
| Mullen (burst) | ECT (stacking) | Wall | Max size sum | Max gross weight | Typical use |
|---|---|---|---|---|---|
| 125 lb | 23 ECT | Single | 40" | 20 lb | Light retail, folding-carton replacement |
| 150 lb | 26 ECT | Single | 60" | 40 lb | Small parcel, light goods |
| 175 lb | 29 ECT | Single | 65" | 50 lb | General light shipper |
| 200 lb | 32 ECT | Single | 75" | 65 lb | The standard single-wall shipper |
| 250 lb | 40 ECT | Single | 85" | 80 lb | Heavier single wall |
| 275 lb | 44 ECT | Single | 95" | 95 lb | Top of the single-wall range |
| 275 lb | 48 ECT | Double | 100" | 120 lb | Entry double wall — the reuse workhorse |
| 350 lb | 51 ECT | Double | 110" | 180 lb | Heavy distribution |
| 400 lb | 55 ECT | Double | 120" | 225 lb | Industrial parts |
| 500 lb | 61 ECT | Double | 140" | 260 lb | Heavy double wall, bulk bins |
| 600 lb | 67 ECT | Triple | 160" | 300 lb | Entry triple wall |
| 700 lb | 71 ECT | Triple | 165" | 600 lb | Export crating replacement |
| 900 lb | 77 ECT | Triple | 170" | 1,200 lb | Heavy bulk bins |
| 1,100 lb | 82 ECT | Triple | 180" | 2,400 lb static | Gaylord standard |
“Max size sum” is length plus width plus depth. Exceeding it voids the certification even if the box is physically capable, which matters in a freight claim.
What a square foot of each build actually weighs.
The number you need to turn a die-line area into a shipping weight, a carbon figure or a freight class. Multiply blank area in square feet by the figure below.
| Construction | lb per ft² | lb per MSF | Caliper | Note |
|---|---|---|---|---|
| Single wall, 32 ECT (C flute) | 0.20 | 200 | 0.16" | Lightest practical shipper |
| Single wall, 44 ECT (C flute) | 0.24 | 240 | 0.17" | Heavier liner, same flute |
| Double wall, 48 ECT (BC) | 0.33 | 330 | 0.30" | The reuse workhorse |
| Double wall, 61 ECT (BC) | 0.40 | 400 | 0.32" | Heavy distribution |
| Triple wall, 71 ECT | 0.48 | 480 | 0.52" | Crate replacement |
| Triple wall, 1,100 lb test | 0.55 | 550 | 0.60" | Gaylord standard |
| Honeycomb panel, 1" | 0.35 – 0.60 | — | 1.00" | Dunnage and display substrate |
Fourteen references worth knowing by number.
Specifying packaging gets much easier once you can name the standard rather than describe the requirement. These are the ones that come up in our quotes and our customers' RFPs.
| Reference | Title | Why it matters here |
|---|---|---|
| ASTM D642 | Compressive resistance of shipping containers | The test behind box compression figures |
| ASTM D4727 | Corrugated and solid fibreboard sheet stock | Material specification for board itself |
| ASTM D5639 | Selecting corrugated box dimensions | How to specify L × W × H correctly |
| TAPPI T 811 | Edge crush test of corrugated board | The ECT number on a Box Maker's Certificate |
| TAPPI T 810 | Bursting strength of corrugated board | The Mullen number |
| TAPPI T 412 | Moisture in paper and paperboard | How moisture content is measured and deducted |
| ISTA 3A / 6 | Packaged-product performance testing | Transit simulation for parcel and distribution |
| ISO 12048 | Compression and stacking tests | International equivalent of ASTM D642 |
| FEFCO / ESBO code | International fibreboard case code | The four-digit style codes we quote against |
| ISPM 15 | Wood packaging phytosanitary measures | Why corrugated avoids an export compliance burden |
| ISRI Scrap Specifications | Recovered paper grade definitions | The #11 and #12 OCC specs we bale to |
| GRI 306 | Waste disclosure standard | The format our diversion statements fit |
| EPA WasteWise | Voluntary waste reduction reporting | Compatible reporting format on request |
| FDA 21 CFR 176 | Indirect food additives: paper and paperboard | Why used board cannot be direct food contact |
Ten conversions we use every day.
None of these are difficult. All of them are regularly got wrong, usually by a factor of 1,728.
| From | To | Factor | Worked example |
|---|---|---|---|
| Cubic inches | Cubic feet | ÷ 1,728 | 48 × 40 × 36 = 69,120 in³ = 40.0 ft³ |
| Square inches | Square feet | ÷ 144 | 13,528 in² = 93.9 ft² |
| Pounds per ft² | Board weight | × area in ft² | 93.9 ft² × 0.55 = 51.7 lb |
| Pounds | Kilograms | × 0.45359 | 51.7 lb = 23.5 kg |
| Inches | Millimetres | × 25.4 | 48" = 1,219 mm |
| Cubic feet | Cubic metres | × 0.02832 | 40.0 ft³ = 1.13 m³ |
| Short tons | Metric tonnes | × 0.90718 | 11,800 tons = 10,705 tonnes |
| Loose OCC volume | Weight | × 80 lb/yd³ | 40 yd³ ≈ 3,200 lb |
| Baled OCC volume | Weight | × 700 lb/yd³ | 2 yd³ bale ≈ 1,400 lb |
| Trailer volume (53') | Usable | × 0.72 | 3,489 ft³ → 2,512 ft³ |
The liners and mediums underneath every box.
Board specification starts one level below the box: which liner, which medium, at what basis weight. Basis weight is stated in pounds per thousand square feet.
| Grade | Basis weight | Fibre | Typical use | Note |
|---|---|---|---|---|
| Kraft liner 26# | 26 lb/MSF | Virgin kraft | Light single wall | Lowest practical outer liner |
| Kraft liner 33# | 33 lb/MSF | Virgin kraft | Standard 32 ECT outer | The commonest liner in North America |
| Kraft liner 42# | 42 lb/MSF | Virgin kraft | 44 ECT and double wall | Noticeably stiffer, better print |
| Kraft liner 69# | 69 lb/MSF | Virgin kraft | Triple wall outer | Gaylord-grade facing |
| Test liner 2 | 27 – 50 lb/MSF | ≥ 80% recycled | General shipper | Most recycled-content board |
| Test liner 3 | 27 – 50 lb/MSF | 100% recycled | Internal and bulk | Lower burst for the same weight |
| Mottled white | 35 – 42 lb/MSF | Mixed | Retail-facing print | White outer, kraft back |
| Semi-chem medium 26# | 26 lb/MSF | Semi-chemical | Standard flute medium | Highest stiffness per weight |
| Recycled medium 23# | 23 lb/MSF | 100% recycled | Economy flute medium | Common in test-liner board |
| Type | Where it is used | Water resistance | Recycling | Note |
|---|---|---|---|---|
| Starch (corrugating) | Liner to medium | Low resistance | Ideal | The standard bond in all corrugated board |
| Hot melt EVA | Manufacturer's joint, cases | Moderate | Tolerated | Fast set; brittle when cold |
| Cold-set PVA | Case sealing | Low | Ideal | Slow set, strong fibre tear |
| Water-resistant starch | Produce board | High | Good | Alternative to wax for damp environments |
| Pressure-sensitive | Tape, labels | Varies | Tolerated in small amounts | Residue downgrades grade A board |
| Stitching (staples) | Manufacturer's joint | Unaffected | Removed in the junk trap | Outlasts glue through reuse cycles |
Seven ways to put a mark on a box.
Ranked roughly by setup cost. The last two are what we use on recovered board — removing somebody else's brand is a different job from applying your own.
| Method | Setup cost | Quality | Recyclability | Use | Lead time |
|---|---|---|---|---|---|
| Flexographic, 1 colour | Low | Basic | Fully | Identification, logistics marks | 3 – 7 days |
| Flexographic, 2 – 4 colour | Medium | Good | Fully | Brand on shipper | 10 – 15 days |
| High-graphic flexo | High | Very good | Fully | Retail-ready packaging | 15 – 20 days |
| Litho-lamination | Very high | Photographic | Reduced | Premium retail display | 20 – 30 days |
| Digital inkjet | None | Good | Fully | Short runs, versioning | 3 – 10 days |
| Blank-out over-print | None | Functional | Fully | Removing a previous owner's brand | Same day |
| Stencil | None | Industrial | Fully | Pool container marking | Same day |