The workhorse carton for e-commerce apparel is the mailer box: a self-locking base, formed in one push, no tape needed at the bottom. It looks like a simple box, but flute grade, size allowance, ink and die accuracy each turn into freight cost, damage rate or unboxing experience when they are wrong.

This guide covers structures, flute grades, how to calculate the size, printing and finishing, and sample approval, so sellers and brands can take a set of parameters straight to a quotation.

What a mailer box is: the structure sets how it forms

A mailer box is a corrugated carton with a built-in locking base: the floor panels interlock, the blank ships flat, and one press forms the bottom without tape. The side flaps on the die layout look like wings, which is where the Chinese trade name comes from.

Three common structures

  • Auto-lock base: the most common; four floor panels interlock for stable load bearing and the fastest forming. Works for single garments and multi-packs.
  • Tuck-top with double tuck: tongues top and bottom, no tape to close. Suits light goods such as T-shirts, underwear and scarves.
  • Compartmented version with inserts: corrugated dividers or paper trays inside for sets, gift boxes and multi-piece kits, at the highest cost.

Flute grades and board: choosing E, B or BC flute

Stiffness comes mainly from the flute, not from the liner grammage. Pick the wrong flute and the box sags and wrinkles at the corners, deforming first on a sorting line. Liners are usually 250-350 g kraft or coated white board: white board for four-colour work, kraft for single colour and a natural look.

Flute Thickness Best for
E flute about 1.5 mm Single T-shirt, underwear, small accessories; flat printing and a near-board feel
B flute about 3 mm The all-rounder: shirts, trousers, dresses, balancing stiffness and volume
BC double wall about 6-7 mm Multi-packs, gift sets and long-haul shipping; highest compression, but the highest volumetric weight

Recycled board costs less but carries surface dust that hurts halftone printing and tape adhesion. If you need a dark solid coverage on recycled board, print a colour sample before committing.

Sizing: work backwards from the folded garment

The size is not based on the flat garment but on the folded, bagged pack plus allowance. Too tight and the fold lines get pressed into the fabric; too loose and the garment slides around and spills out on opening.

  • Measure the folded, bagged pack first, including the bag and the hang tag in the thickness.
  • Inside size = pack size + 3-5 mm per side; outside size = inside size + two board thicknesses.
  • Check volumetric weight: L x W x H (cm) / 6000, billed on the greater of that and actual weight. Near a threshold, shaving 1 cm can drop a freight band.
  • Keep a range to two or three sizes: less die cost, less stock pressure, and easier matching with carrier box sizes.

Printing and finishing: spend where the box is opened

An e-commerce carton has a large print area and little copy: the easiest place to build brand presence, and the easiest to ruin. Fix the printing method first, then the details.

  • Single-colour water-based printing: lowest cost, shortest lead time, dependable in black or a brand colour. Right for routine shipping above a thousand units a month.
  • Four-colour offset laminated to corrugated: good colour fidelity for gift boxes and launches, at the price of high minimums, long lead times and costly revisions.
  • Windows and die-cutting: show the garment, but you add a die and a film patch, and the window must clear the label and tape zones.
  • Inserts and cards: a thank-you card plus a size or care card costs little and moves repeat purchase and user photos the most.
Note: corrugated liners absorb ink unevenly, so large dark solids show streaks and misses. With dark artwork, prefer white space plus single-colour line work over a full solid.

Sampling and approval: three steps not to skip

  • White sample: unprinted, it only proves the size, the lock engagement and that it forms smoothly. Fastest and cheapest.
  • Colour sample: confirm spot colour and solids. On corrugated the result usually reads 5-10% darker than the same artwork on card.
  • Transit test: ISTA 1A drop on one corner, three edges and six faces, then 24 hours of stacking to see if the bottom corners crush. Far more reliable than eye judgement.

Incoming inspection needs four checks: inside dimension within plus or minus 2 mm, locks that do not pop, register on colour, and board free of moisture blisters. Put these on the inspection sheet and they beat any verbal promise.

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Need a mailer box for a new season? Send the folded pack size, units per box and the print effect you want; we start with a white structure sample to confirm size and lock, then quote production.

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