Packaging Board Chart

32 ECT is an edge crush strength of 5.6 kN/m (kilonewtons per meter). It is the standard single wall grade for US shipping boxes, sitting in the same Item 222 row as 200 lb burst test, and is rated for boxes up to 65 lb (29.5 kg) gross weight. Packwire mailer and shipping boxes are both 32 ECT.

It is a Mullen burst test rating: the board withstands 200 pounds per square inch (1,379 kPa) of pressure on a Mullen tester before the facing ruptures. It measures how well the facings resist bursting, not stacking strength. Item 222 accepts 32 ECT as the alternative in the same row, and both carry a 65 lb maximum gross weight.

Use ECT when boxes will be stacked on pallets, because edge crush predicts stacking strength. Burst measures how well the facings resist rupturing, which relates only indirectly to rough handling. It cannot be run on triple wall and is unreliable on heavy double wall. Most North American box makers test to ECT today; when a Box Manufacturer’s Certificate is printed, it shows one of the two.

E-flute is 1/16 inch (0.0625 in), or 1.6 mm, with about 90 flutes per foot (295 per meter). It is the thinnest common box flute and the one used for printed mailer boxes, including Packwire mailers.

B-flute is 1/8 inch (0.125 in), or 3.2 mm, with about 47 flutes per foot (154 per meter). Packwire shipping boxes are B-flute.

At the same liner weights, B-flute is stronger. It is twice as thick, so it is stiffer, resists crushing better and stacks higher. E-flute gives a flatter surface for print and folds more cleanly, which is why mailers and retail boxes use it. Both can be made to 32 ECT; the flute changes how the box behaves at that rating, not the rating itself.

Single wall has one fluted medium between two liners. Double wall has two mediums and three liners, usually a B and a C flute (BC) or an E and a B (EB). Double wall carries more compression load and is rated from 80 lb to 180 lb gross, versus 20 lb to 120 lb for single wall.

That is the UK and EU way of writing a corrugated grade: outer liner grammage and type, flute, inner liner grammage and type. 125 K/T B is a 125 gsm kraft outer liner, B-flute, 125 gsm test (recycled) inner liner. North American board is specified by tested strength instead, so 150 K/T B is roughly a 29 to 32 ECT single wall.

Chinese and wider Asian factories grade each liner with a letter, K for the strongest kraft liner (about 250 to 300 gsm), then A (175 to 200 gsm), B (125 to 150 gsm) and C (100 to 120 gsm). The equals sign stands for the flute between them, so K=A is a kraft outer liner and an A-grade inner liner. 3-ply is single wall, 5-ply is double wall, 7-ply is triple wall. A=A or K=A 3-ply is roughly a 29 to 32 ECT North American single wall.

Ask the overseas supplier for two things: the liner and medium grammage in gsm, and a tested ECT figure for the finished board, not one calculated from the papers. Finished board can test roughly 10 percent above or 20 percent below a paper-based estimate, so a calculated 32 could test as low as 26. Then read across this page: 150 gsm liners on B- or C-flute land near 29 to 32 ECT (note that a European ECT figure, measured on a shorter sample, is not on the same scale as a US one), and K=A or A=A 3-ply is in the same range. A North American box is made from board tested to a published grade and can carry a Box Manufacturer’s Certificate stating that grade and its maximum gross weight; an imported board is rarely tested that way, and humidity takes a large bite out of strength: box compression drops about 30 percent at 80 percent relative humidity and 45 percent at 90 percent, conditions a container crossing can reach. Packwire boxes are made in the USA from 32 ECT board.

Yes. M weight is the weight in pounds of 1,000 sheets of paper at its basic size, where basis weight counts 500 sheets, so the M figure is double: 80 lb text is 160M, 100 lb text is 200M. Canadian paper merchants and many printers quote M weight; American mills quote basis weight; the rest of the world quotes grammage, and 80 lb text (160M) is about 118 gsm. The litho wrap on Packwire rigid boxes is 80 lb text, 160M.

16 pt is 0.016 inch, or 0.41 mm. For SBS paperboard that is about 350 gsm or 129 lb cover. Grammage varies about 10 percent by mill at the same caliper. Packwire folding cartons use 16 to 18 pt SBS.

Divide gsm by the board’s density in grams per cubic centimetre, then by 1,000. For SBS at about 0.87 g/cm³, 350 gsm is about 0.40 mm (16 pt). For chipboard at about 0.65 g/cm³, 1,000 gsm is about 1.5 mm (60 pt). Caliper is the better spec to order by, because grammage alone does not fix stiffness.

Corrugated board, paperboard and chipboard. Corrugated has a wavy fluted layer between flat liners, which makes it stiff and cushioning, so it is used for shipping and mailer boxes. Paperboard is a solid sheet with no flutes, built to print and fold: SBS is white all the way through and used for premium retail cartons, while recycled CCNB has a white face over a gray back and costs less. Chipboard, or grayboard, is a thick, dense recycled board wrapped in printed paper to make rigid gift boxes.

Primary packaging holds the product itself and is what the customer sees or unboxes, such as a folding carton, a rigid gift box or a printed mailer. Secondary packaging groups primary packs or ships them, such as a corrugated shipping box, a case of cartons or a display tray. Tertiary packaging moves goods in bulk: pallets, corrugated pallet boxes, tier sheets, corner boards and stretch wrap. Paperboard and chipboard are almost always primary; corrugated is the usual secondary and tertiary board, and becomes primary too when a printed mailer is the product box, which is common in ecommerce.

In everyday speech, usually yes: most people say cardboard box when they mean a corrugated box. In the packaging trade, cardboard is a loose word for any heavy paper-based board, so it can also mean paperboard, such as a retail product carton, or chipboard. When ordering, name the board: corrugated with a flute and ECT grade, paperboard in points, or chipboard in points or millimeters.

Box sizes are written length × width × depth, in that order, and are normally inside dimensions. Length is the longer side of the opening, width the shorter, and depth runs at right angles to both. Because the opening decides which side is which, an end-loading box is written differently from a top-loading box of the same shape. Inside dimensions make sure the product fits; outside dimensions matter for pallets and carrier size limits, so tell the box maker which one is critical.

Four. Direct flexo prints on the finished board and is the most common. Preprint flexo prints the liner roll before it becomes board, for high-volume runs. Litho lamination or a litho label glues an offset-printed sheet to the board for photographic detail of about 200 lines per inch. Digital inkjet needs no plates, so there is no plate cost and short runs make sense. Smaller flutes such as E and F give a flatter print surface than B or C.

Plain corrugated recycles easily. Wax is the problem, because it interferes with repulping. Water-resistant alternatives such as film laminations and water-based treatments can be certified as repulpable and recyclable, and more than 70 had been certified by 2024. Printing, tape and paper labels do not stop a box from being recycled; plastic laminates, foil and plastic windows can.

CCNB is clay-coated news back: a recycled paperboard with a white clay-coated printing face and a gray back, usually 16 to 30 pt. North American mills also call it CRB, coated recycled board; European quotes call it white-lined chipboard (GD2 or GD3) and Asian quotes gray-back duplex board. It costs less than SBS but is less stiff at the same caliper, so it suits budget cartons, sleeves and the inner platforms of rigid boxes. Its kraft-backed cousin is CCKB.

A rigid or set-up box is a grayboard core wrapped in printed paper. The core is dense recycled chipboard, 30 to 120 pt (0.8 to 3 mm), gray throughout and not printable on its own; Packwire uses 50 pt and steps up on larger sizes. Premium boxes use higher-density bookbinding board for stiffness, or black through-dyed board under dark wraps. The wrap is litho-printed paper, 80 lb text (160M, 118 gsm) at Packwire, or 128 to 157 gsm art paper on Asian quotes. Inner platforms and trays are usually CCNB or CCKB duplex board.

SBS is the board itself: solid bleached sulfate, a white virgin-fiber paperboard. C1S and C2S describe its coating: coated one side or coated two sides. A C1S SBS carton prints on the coated outside and has plain board inside; C2S prints on both faces.

Mailer boxes are E-flute single wall corrugated, 32 ECT, 1/16 in thick, in White Board (mottled white liners), Kraft Board (natural kraft liners) or SuperGloss (clay-coated gloss liners). Shipping boxes are B-flute, 32 ECT, 1/8 in, in White Board (mottled white outer liner over kraft) or Kraft Board. Folding cartons are 16 to 18 pt SBS paperboard. Rigid boxes are 50 pt chipboard wrapped in 80 lb litho-printed paper, with thicker board on larger sizes.

The Item 222 and Rule 41 table sets two limits for every grade: a maximum gross weight and a maximum outside size, length plus width plus depth. A box must satisfy both. A bigger box has longer unsupported panels that bulge and crush sooner, so a 57 lb case measuring 39 + 23.6 + 18 = 80.6 united inches needs 250# or 40 ECT even though its weight alone would fit the 200# row. Item 222’s size extension formula lets an underweight box go a little over: half its weight shortfall, as a share of the row’s limit, is added to the size limit. That stretches the 200# row to about 79.6 in for a 57 lb box, still just short. Large retailers’ routing guides check cases against this table and usually ask for 200# or 32 ECT board on shipping cases.

No. The Box Manufacturer’s Certificate, the round stamp stating the board test, size limit and gross weight, is a voluntary mark under NMFC Item 222 and UFC Rule 41, not a legal requirement. It matters for less-than-truckload common-carrier freight, where a box that matches its certificate keeps the carrier’s damage liability and freight rates intact. Full truckloads, parcel shipments and a shipper’s own fleet do not need it, which is why many printed mailers and retail boxes carry none. Packwire prints one when an order’s volume and spec call for it.

Somewhere between about 40 and 100°F with relative humidity around 30 to 70 percent, off the floor and away from exterior walls. Humidity is the variable that matters most: a box sitting in 80 percent humidity has lost close to a third of its stacking strength. Empty boxes do not expire; if they are dry, square and uncrushed, they are good to use.

RSC stands for regular slotted container, code 0201 in the international FEFCO case code system and the most common corrugated box style. It is made from one scored and slotted sheet joined at one corner, with four flaps top and bottom that are all the same depth, so the two outer flaps meet in the middle. It wastes very little board. Packwire shipping boxes are RSCs.

The Item 222 table rates 32 ECT single wall to 65 lb (29.5 kg) gross weight, and that is what a Box Manufacturer’s Certificate prints when one is used. In practice the flute and the box style matter too. Packwire recommends keeping E-flute mailer boxes under about 40 lb and B-flute shipping boxes under about 60 lb, because the thinner E-flute and the mailer’s tuck-top closure carry less than a taped C-flute shipper of the same rating.