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, equivalent to the older 200 lb burst test rating, 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 before its face bursts. It measures puncture resistance, not stacking strength. The ECT alternative to 200# single wall is 32 ECT, and both carry a 65 lb maximum gross weight on a North American Box Maker’s Certificate.

Use ECT when boxes will be stacked on pallets, because edge crush predicts stacking strength. Use the burst test when boxes ship as single parcels and take drops and impacts, because it predicts puncture resistance. Most North American box makers test to ECT today; when a Box Maker’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 resists crushing and punctures 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 roughly doubles stacking strength 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 an ECT figure for the finished board. Then read across this page: 150 gsm liners on B- or C-flute land near 29 to 32 ECT, 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 Maker’s Certificate stating that grade and its maximum gross weight; an imported board is rarely tested that way, and six weeks at sea in humid containers can cost it 10 to 20 percent of its edge crush strength before it reaches you. 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.

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 cereal and dry-goods 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 in needs 250# or 40 ECT even though its weight alone would fit the 200# row. Large retailers’ routing guides check cases against this table and usually ask for a Box Maker’s Certificate of at least 200# or 32 ECT on shipping cases.

The Item 222 table rates 32 ECT single wall to 65 lb (29.5 kg) gross weight, and that is what a Box Maker’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.