One level below the box: the paper itself.
Most packaging conversations stop at 'double wall, 48 ECT'. Underneath that are two liner grades, a medium, a basis weight for each and an adhesive — and each of those decisions shows up in how the box behaves on your dock.
Specify a board
Tell us the load, the stack height and the handling, and we will spec the board.
Straight to the grading floor at 9869 Meeks Blvd, St. Louis, MO 63132.
Or email sales@reboxesmarket.com. We have no phone line — dimensions and counts survive much better in writing.
Not sure of the size?
Fold a box in the browser, read off the cube and pallet fit, and send the spec straight through.
Basis weight is the hidden number
Liner and medium are traded by basis weight: pounds per thousand square feet, written as 33#, 42#, 69# and so on. A 32 ECT box might be built from 33# kraft liner on both faces with a 26# semi-chemical medium. Step the outer liner to 42# and the box stiffens noticeably without changing its flute or its wall count.
This matters for reuse specifically. Heavier liner resists the surface abrasion that turns a grade-A container into a grade-B one, and it survives label removal at the re-face station far better. If you are specifying new board for a pool, this is the lever worth pulling.
Kraft versus test liner
Kraft liner is made predominantly from virgin fibre and is stiffer and stronger for a given basis weight. Test liner is made predominantly from recycled fibre. Most US-made board uses test liner for at least the inner face and often both, which is why domestic board runs 70 – 90 per cent recycled content as standard rather than as an upgrade.
The honest trade-off: for the same basis weight, high recycled content gives slightly lower burst strength, because repeated pulping shortens fibres. We would rather step up a grade than let a recycled-content specification quietly cause product damage.
Semi-chemical medium
The fluted medium does most of the structural work and almost nobody specifies it. Semi-chemical medium has the highest stiffness per unit weight and holds flute geometry best under compression and humidity. Fully recycled medium is cheaper and noticeably less rigid, which shows up as earlier flute collapse in a reuse cycle.
Adhesive, and the recycling consequence
The liner-to-medium bond is starch, which is ideal for recycling because it disperses in a pulper without residue. Everything added afterwards — hot melt at the manufacturer's joint, pressure-sensitive tape, labels — is a prohibitive in small quantities and a problem in large ones. Water-activated paper tape is the only closure that goes into the bale without being a contaminant.
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 |
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 |
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.
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 |
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 |
Board specification.
What does 33# actually mean?
Pounds per thousand square feet of that single paper component. A 33# liner weighs 33 lb per MSF. It is a weight, not a strength, though the two correlate closely within a fibre type.
Should I specify the liner grades myself?
For a one-off order, no — specify the performance (ECT or Mullen, and your real stack height) and let the converter choose. For a reusable container pool, yes, because liner weight materially affects how many trips you get.
Is 100% recycled board weaker?
For the same basis weight, slightly — particularly in burst strength. The fix is to step up basis weight or flute rather than to accept lower performance. We will tell you what that costs before you commit.
Why does my box specification not list the medium?
Because almost nobody asks. The medium is where a converter can quietly save money, and on a reuse programme it is where you will feel it first as earlier flute collapse.
Does print affect recyclability?
Flexographic print, including heavy coverage, recycles normally — the ink disperses and is removed in cleaning. Litho-lamination is the problem, because you have bonded a coated sheet onto corrugated and the mill has to separate two materials.
What tape should we use if boxes come back to us?
Water-activated paper tape, without hesitation. It bonds into the fibre rather than sitting on it, it is far harder to tamper with, and it goes into the OCC bale as part of the box rather than as a contaminant.