Buyer's Guide · E-commerce packaging
Short answer: for most e-commerce mailers you need E-flute (about 1.5 mm) for subscription-style boxes and B-flute (about 3.0 mm) for heavier goods, both single wall at 32 ECT or above (typical). Specify inside dimensions, flute, ECT and print sides — those four lines are enough for an accurate quote.
Last updated: · 7 min read · By the Renjie editorial team · Includes: flute table, ECT rules of thumb, freight math
A corrugated mailer box is a one-piece corrugated board box whose side walls fold up and tuck or fold in without glue, tape or a separate lid. It is the shipping container and the unboxing experience in one. That is the core difference from folding cartons, which are paperboard, thinner and made for the retail shelf — a carton protects against shelf handling, a mailer protects against a courier conveyor. If your product ships directly to the consumer, the mailer is usually the right outer box; if it ships to a retailer inside a master carton, a carton plus a gift box may serve better.
Flute is the wavy paper layer glued between two liners, and its height decides stiffness, print smoothness and how much space the box consumes when folded. The Wikipedia corrugated fiberboard overview covers the full alphabet; these three do nearly all e-commerce work (typical values, illustrative):
| Flute | Height (mm) | Walls | Best for | Print surface |
|---|---|---|---|---|
| E | ~1.5 | Single | Subscriptions, cosmetics, electronics accessories — light to medium loads | Smooth; holds fine print and laminated wraps |
| B | ~3.0 | Single | Books, apparel, general e-commerce up to a few kg | Slight fluting visible on flat tints |
| C | ~4.0 | Single | Master cartons and heavier direct-ship goods | Rougher; usually overprinted or labeled |
Double wall (BC, roughly 7 mm) exists for genuinely heavy or fragile loads, but it costs more, weighs more and eats freight volume. Most D2C mailers should start at E or B.
ECT — edge crush test — measures how many kilonewtons per meter a vertical column of the board resists before crushing, and it is the honest strength spec for corrugated board. The old "200# burst" ratings still circulate, but ECT is what modern buyers put on the RFQ. As a rule of thumb (typical, illustrative): 32 ECT single wall handles standard D2C parcels up to roughly 10 kg gross; 44–48 ECT or double wall handles dense multi-item orders. Two cautions from practice: a taller box walls carry load better than a wide flat one of the same board, and repeated handling — the courier reality — means margin beats minimum. If you also ship books in bulk, our LCL vs FCL shipping guide covers the master-carton side of the same decision.
Carriers do not bill by weight alone — dimensional weight divides the box volume by a carrier factor, so an oversized mailer is taxed as if it were heavier than it is. The Wikipedia dimensional weight explainer shows the formula; the practical rule is simpler: order the smallest inside dimension that fits the product plus a 5–10 mm cushion (typical). Every 10 mm of extra depth on a 250 × 180 × 100 mm mailer adds roughly 2–3% to its billable volume (illustrative) — which compounds across thousands of parcels. Give the printer the product's exact dimensions and let the die-line be engineered outward from them, not the other way round.
Corrugated is one of the most recycled packaging materials, which is why EU-facing brands start their packaging file here. Under the EU waste framework — where the European Commission's Waste Framework Directive overview sets the waste hierarchy and the Extended Producer Responsibility principle — your importer may need recyclability and EPR registration documents for the mailer, alongside the PPWR paperwork we detail in the PPWR documents guide. If you want certified fiber, FSC-certified liner board is available on request with chain-of-custody documentation — see fsc.org — and the FSC claim is printed with the license code, not assumed.
Ready to spec yours? Send product dimensions and monthly volume through the quote form — we will return flute and ECT options with the freight impact, and compare the mailer against a wrap-and-carton setup where that is cheaper. For shelf-facing boxes that pair with your mailer, see our magnetic gift box specs guide.
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