Corrugated Boxes Explained: Mailers, Shipping Cartons & Lidded Boxes

"Corrugated box" is not one product. The wave-shaped layer sandwiched between the liners — the flute — decides how thick the box is, how much it carries, how it prints and what it costs to ship. Pick the wrong flute and you either pay freight on air or watch boxes buckle on a pallet. Below: what E, B, C and BC actually mean, how mailer boxes, shipping cartons and lidded boxes each get specified, and when each one is the right answer.

The short answer

• Custom mailer boxes, retail-ready packaging → E-flute (about 1.5 mm). Slim, crisp to print on, ships flat.
• General shipping cartons, e-commerce outer boxes → B-flute (about 3 mm). The all-rounder.
• Heavy or stacked loads → BC double wall (about 6–7 mm). Two flutes laminated together.
• Not sure what your load needs → tell us the packed weight and stacking conditions; we test before quoting.

What a flute actually is

Corrugated board is three layers: a liner, the fluted (wavy) medium, and another liner. The flute is that middle wave. A taller wave gives more cushioning and vertical stacking strength but a thicker, heavier board with a rougher print surface. A shorter wave gives a thinner, flatter sheet that prints beautifully and saves freight volume — but carries less. Everything below is that one trade-off, applied four ways.

The four flutes that matter for export buyers

E-flute — about 1.5 mm

The thinnest common flute, and the one behind most custom mailer boxes you see from e-commerce and subscription brands. Because the flute is short, the surface is comparatively smooth, so it takes direct flexographic printing, litho-lamination and even fine detail far better than thicker flutes. It is rigid enough to protect apparel, cosmetics, electronics accessories and similar light-to-medium goods, and because it is thin, more boxes fit in a container — which matters when freight is part of your landed cost.

B-flute — about 3 mm

The workhorse. Good all-round cushioning and stacking strength, a flatter surface than C-flute for printing, and a wall thickness that keeps boxes efficient to ship flat. If you order "corrugated shipping boxes" without specifying a flute, B is very likely what you will get. Standard choice for e-commerce outer cartons, die-cut mailers for heavier goods, and point-of-sale displays.

C-flute — about 4 mm

Slightly thicker than B with more cushioning, and the default for plain brown RSC shipping cartons — the everyday "carton box" of global trade. Print quality is noticeably rougher than B or E, which is fine for a shipping carton and wrong for a shelf-facing box. Many export cartons are specified in C or B purely on cost and stack performance.

BC double wall — about 6–7 mm

A B-flute and a C-flute laminated into one board. The two flutes work together: one absorbs shock, the other carries stacking load. This is what you specify when cartons are palletised high, container shipped, or loaded heavy — ceramic tableware, glass jars, canned goods, machinery parts. It costs more per box and eats more freight volume, so it is a decision to make against the real load, not a default.

Side-by-side comparison

Strength figures also depend on liner quality (e.g. 175K vs 250K kraft liner), board combination and box geometry — two BC boxes with different liners are not the same box. Treat the table as a starting point and have the final combination confirmed against your load.

How printing works on corrugated

• Direct flexo — printed straight onto the board. Most economical for 1–3 colour designs; fine detail is limited by the board surface.
• Litho-lamination — a printed art paper sheet is laminated onto the corrugated. This is how premium mailer boxes get full-colour, photographic print quality; usually paired with E-flute.
• Preprint — the liner is printed before the board is made, for very large runs of identical cartons.

If your design has gradients, small text or heavy ink coverage, ask for litho-lamination on E- or B-flute rather than fighting the limits of direct flexo — the unit cost difference is smaller than most buyers expect at 5,000 pcs and above.

Corrugated mailer boxes

A corrugated mailer box is a die-cut, self-locking box designed to be shipped as the outer pack and opened by the end customer — no void fill, no separate shipping carton. Almost all of them are E-flute or B-flute, printed inside and out, and delivered flat so you store and freight air, not boxes.

• E-flute mailer — the premium look. Thin enough for litho-laminated full-colour print, rigid enough for cosmetics, apparel, electronics accessories and subscription kits.
• B-flute mailer — the durable one. Choose it when the box travels alone through couriers, when the packed weight passes roughly 3–4 kg, or when corners take repeated drops.
• What drives the price — die shape and material yield, number of print colours, and whether you need an insert (card tray, foam or moulded pulp). A custom die is a one-off cost shared across the whole run, so it barely moves the unit price at 5,000 pcs and above.

If you are comparing a mailer against a folding carton: a carton is a shelf box that needs an outer shipper; a mailer is the shipper. E-commerce brands usually end up wanting the mailer.

Corrugated shipping boxes

Corrugated shipping boxes — RSC (regular slotted container) cartons, die-cut outers, and the pallet-load export cartons behind them — are bought on a different set of numbers than retail boxes. Nobody sees the print. What matters is compression strength, board caliper, and how many boxes fit in a container.

Two practical notes we give every buyer: quote the packed weight, not the product weight, and state the pallet pattern and stack height. Those two numbers decide the board far more than the product does. Also compare on landed cost — a slightly cheaper box that needs extra void fill, or that is 2 mm thicker and costs you container space, is not the cheaper box.

Boxes with lids: two ways to close a corrugated box

Buyers searching for corrugated boxes with lids are usually after one of these, and they are not the same product:

• Lid-and-base (two-piece / telescoping) box — a separate base tray and a lid that slides or drops over it. The most retail-looking option, and the easiest to open and re-close. Common in E-flute for gift sets, apparel, cosmetics and corporate kits. Costs slightly more than a one-piece mailer because it is two pieces.
• Tuck-top / tuck-end box with a lid flap — one piece of board, one flap folding shut. Cheapest, packs and stores flattest, and a good fit for lighter goods or where the box goes inside a shipper anyway.
• RSC carton with a lid — the plain shipping carton whose top flaps form the lid. Not a display box, but if the requirement is simply "lid, stacks well, cheap", this is the answer.

Add a magnetic closure or a ribbon pull and the same box reads as a rigid gift box — worth asking about if your product sits above roughly $30 retail and the unboxing matters.

Is there such a thing as a corrugated plastic mailer?

Strictly, no — corrugated plastic (twin-wall polypropylene, often called Correx or Coroplast) is a completely different material from corrugated paperboard. It shares only the wavy core idea: the sheets are extruded plastic, waterproof, reusable and about 3–5× the cost of an equivalent paperboard box.

What ships as a "corrugated plastic mailer" today is usually one of two things, and it is worth knowing which you actually want:

• Paperboard mailer with a water-resistant coating or liner — the recyclable option. Handles rain and damp handling without turning into a plastic box. This is what most brands asking for this product really need, and it keeps the parcel kerbside-recyclable.
• Genuine twin-wall PP mailer — chosen for returnable, reusable or genuinely wet logistics loops (reusable transport packaging, cold chain, heavy-duty reuse). Not recyclable in normal paper streams and not printable to retail standard.

Choosing by scenario

How we quote corrugated boxes

We are a custom paper packaging manufacturer based in Quanzhou, China. Send us the product, dimensions, packed weight and quantity, and the quotation will state the board combination explicitly — flute, liner weights and construction — so you can compare like for like with any other supplier. MOQ from 5,000 pcs, free pre-production sample in about 7 days, and a written quotation within one working day.