An e-commerce box does two jobs that pull in opposite directions. It has to look like your brand when the customer opens it, and it has to survive a parcel network that drops, stacks and shakes it on its own, without a pallet or a shrink-wrapped load around it.
This guide is for online brands, subscription businesses and fulfilment teams that want printed mailer boxes or plain shipping cartons made in Asia. It covers how to specify the corrugated board, how to name the box style so every factory quotes the same thing, which transit tests to ask for, and how to plan stock so you never run out of boxes before you run out of product.
💬 Need mailer boxes in several sizes, printed or plain? Send us your product dimensions, weights and current box, and we will look for corrugated converters in Asia that fit the job. Tell us about your boxes.
Specify the corrugated board, not just “strong”
A corrugated board is defined by its wall construction, flute profile and the liners on each side; write all three on the specification and ask for a test value the factory will hold to.
Corrugated board is a fluted paper sandwiched between flat liners. The three choices that change its behaviour are:
- Wall construction. Single-wall board has one fluted layer; double-wall and triple-wall boards add more. Light consumer goods often ship in single-wall mailers, while heavy or fragile items may need double-wall.
- Flute profile. Flutes are named by letter, such as E, B and C, and differ in height. A low flute gives a smoother surface for printing and a neater fold; a taller flute cushions and stacks better. Factories also combine two flutes in double-wall boards.
- Liners. The outer liner can be white or brown (kraft), coated or uncoated, virgin or recycled fibre. A white outer liner takes colour print better; a kraft liner gives a natural look but darkens printed colours.
| Choice | Lower setting | Higher setting | What it changes |
|---|---|---|---|
| Wall | Single-wall | Double-wall | Stacking strength, weight, freight volume |
| Flute | Low (fine) flute | Tall flute | Print quality versus cushioning and compression |
| Outer liner | Kraft, uncoated | White, coated | Print sharpness and colour, scuff resistance |
| Inner liner | Plain | Printed | Unboxing effect, extra print cost |
Do not accept “strong board” or a factory’s internal code as a specification. Ask for the board make-up and a measured value, such as the edgewise crush resistance of the board, and agree the test method. ISO 3037:2022 is the current ISO method for measuring the edgewise crush resistance of corrugated fibreboard, and the factory or a test lab can report against it.
Name the box style with a code
Use the International Fibreboard Case Code to name the box style, and give dimensions as internal length, breadth and height, so every factory quotes the same construction.
“Mailer box” can mean a folder-type box with a tuck-in lid, a box with dust flaps, a crash-lock style or a plain slotted carton. The International Fibreboard Case Code, published by FEFCO and ESBO, gives each construction a four-digit number so it can be ordered without long descriptions. Its groups include:
- 02, slotted-type boxes: one piece with a glued, stitched or taped joint and top and bottom flaps, shipped flat and closed with the flaps (0201 is the familiar regular slotted carton).
- 03, telescope-type boxes: a lid and/or base telescoping over the body.
- 04, folder-type boxes and trays: usually one piece, with the bottom hinged to form the side walls and cover, and locking tabs or handles in some designs. Many die-cut mailer boxes are folder-type designs, and 0427 is one of the designs in this group.
- 07, ready-glued cases: shipped flat and set up by simply opening them.
The Code says dimensions are, unless otherwise specified, internal dimensions in millimetres given as length x breadth x height, where length is the longer side at the opening. Use the same convention in your purchase order. A box quoted on external dimensions by one factory and internal by another is not the same box.
Ask each factory to send the dieline for the code it proposes, and approve it before printing. Our guide to dielines, artwork and colour proofing covers that step.
Fit the box to the product, then to the network
Size the box from the product plus its protection, keep empty space to what the protection needs, and remember the EU will set a maximum empty-space ratio for e-commerce packaging.
An oversized box costs more to ship, needs more void fill and lets the product move. Measure the product in its retail pack, add any insert or cushioning, and then size the box. Keep a small set of sizes that covers your range rather than a box for every SKU.
Empty space is becoming a legal point as well as a cost point. Regulation (EU) 2025/40 on packaging and packaging waste applies from 12 August 2026. Its Article 24 requires economic operators who fill grouped, transport or e-commerce packaging to keep the maximum empty space ratio to 50 %, by 1 January 2030 or three years after the Commission’s implementing acts on the calculation method, whichever is later. Space taken by void fill, such as paper, air cushions or foam chips, counts as empty space under Article 24(3), and operators that ship in the product’s own sales packaging are exempt from the 50 % ratio under Article 24(5). The Regulation gives the Commission until 12 February 2028 to adopt the method, so confirm the current rule in the market where you sell before you lock in a size range for Europe.
Transit testing: which test, and who runs it
Name a recognised transit test in the purchase order, decide whether the factory or an independent lab runs it, and test the packed product, not the empty box.
A box that passes a board test can still fail when the product inside shifts. Transit tests put the complete packed unit through drops, vibration, compression and climate, in a defined sequence.
| Test or standard | What it covers | When buyers use it |
|---|---|---|
| ISTA 3A | General simulation for individual packaged products shipped through a parcel delivery system, 150 lb (70 kg) or less; standard, small, flat and elongated packages | Direct-to-consumer parcels |
| ISTA 6-series | Member performance tests that reflect a specific retailer’s or carrier’s supply chain | When a marketplace or retailer names its own protocol |
| ISTA 1- and 2-series | Non-simulation integrity tests and partial simulation; screening and design refinement | Early development and quick checks |
| ASTM D4169 | Practice for performance testing of shipping units through a sequence of distribution hazards | Shipping units and larger cartons; it points to ASTM D7386 for single parcel shipments |
| ASTM D642 | Test method for compressive resistance of shipping containers, components and unit loads | Stacking strength in storage and containers |
| ISO 2248:1985 | Vertical impact test by dropping, for complete filled transport packages | Drop resistance |
ISTA’s own description says its 3-series tests simulate the motions, forces and conditions of transport and can be used to predict damage risk, while its 1-series tests are screening tests that do not simulate real events. If you sell through a marketplace or retailer that publishes its own packaging requirement, follow that requirement first; several have ISTA 6-series protocols written for their distribution systems.
Practical points:
- Test with real or production-equivalent products in the box, with the insert and void fill you will use.
- Agree the pass criteria before testing: no product damage, no box failure that exposes the product, and what level of cosmetic damage is acceptable.
- Retest when you change the board, the box style, the product or the packing method.
- Keep the test report with the approved sample.
💬 Want your mailer boxes tested before you order volume? We arrange transit testing with the factory or an independent lab and compare the results with you. Ask us about testing.
If your products are long, curved or fragile, our article on packaging for online marketplaces shows how to match the inner protection to the product type.
Printing on corrugated
Corrugated mailers are printed either directly on the finished board or on a liner that is laminated to the flute; the method sets how fine your artwork can be.
There are two broad routes:
- Direct printing on corrugated board, usually flexographic. Suited to one- or two-colour logos, line art and plain shipping cartons. Fine text, gradients and photographs reproduce less sharply, and the flutes can show through as faint lines.
- Litho-lamination, where a printed paper liner is laminated to the corrugated board. Suited to full-colour, photographic or premium mailers, with more set-up and material.
- Digital printing on corrugated is available from some converters and suits short runs or many designs, but check colour consistency between runs.
Printing on the inside of a mailer creates an unboxing effect and adds cost. A kraft outer with a printed white inside is one way to keep the outside plain and the inside branded.
Printed colour behaves differently on kraft and on white liners. Approve colour on the actual board, not on a paper proof. If you also want a recycled or FSC statement on the box, see our guide to recycled and FSC claims by market.
Stock, reorders and keeping boxes consistent
Plan box stock against your sales forecast and the factory’s full cycle from order to delivery, and reorder on the approved specification so each batch matches the last.
Running out of boxes stops dispatch as surely as running out of product. A few habits help:
- Set a reorder point based on how many boxes you use per period and how long a full cycle takes, from purchase order to boxes on your shelf. Ask the factory for its current cycle on each order; it changes with season and paper supply.
- Store boxes flat, dry and off the floor. Corrugated board absorbs moisture, which weakens it. Boxes stored in a humid warehouse may fail tests they passed when new.
- Reorder on the same specification. Quote the box code, board make-up, test value and approved sample reference on every reorder, so the factory cannot quietly substitute a lighter board.
- Check each batch. Measure internal dimensions, check print against the approved sample and, for important lines, retest the board value. Our note on pre-shipment inspection and AQL explains how to set sample sizes.
- Ship boxes with other goods. Boxes are light and bulky; combining them with products from other suppliers can reduce freight cost per unit. Our guide to consolidating Asian suppliers in one shipment explains how.
For customs, cartons, boxes and cases of corrugated paper or paperboard fall under Harmonized System subheading 4819.10. Confirm the code and the rate in the market where you import.
Frequently asked questions
1. Which flute should I choose for a printed mailer box?
A low, fine flute prints more sharply and folds more neatly; a taller flute protects better. A fine flute for light products and double-wall board for heavy ones is a reasonable starting point. Test with your product.
2. What does a box style code like 0201 or 0427 mean?
It is a design number from the International Fibreboard Case Code. 0201 is a regular slotted carton; 0427 is one of the designs in the folder-type group, where many die-cut mailers sit. Ask the factory which code its die follows.
3. Do I need an ISTA test for e-commerce boxes?
It is not a legal requirement in itself, but a named test gives you and the factory a clear pass standard. Some marketplaces and retailers set their own packaging requirements, so check theirs first.
4. Why did my boxes pass testing but fail in the warehouse?
Humidity is a common cause. Corrugated board loses strength when it absorbs moisture. Store boxes dry and off the floor, and ask the test lab to condition samples before testing.
5. Will EU rules limit how big my mailer box can be?
Regulation (EU) 2025/40 sets a 50 % maximum empty-space ratio for e-commerce packaging from 2030 at the earliest, once the calculation method is adopted. Confirm the current rule in the market where you sell.
Summary
Specify the board make-up, name the box with a style code, size it to the protected product and prove it with a named transit test. Then reorder on the same specification so every batch performs like the one you approved.
Sunsho Trade is a trading company, not a factory. For mailer boxes and shipping cartons we find and vet converters in Asia, collect quotations on identical specifications, arrange samples, transit tests and inspection, and plan delivery with your other goods.
💬 Ready to source mailer boxes? See our custom packaging service, or send us your box sizes and products and we will come back with options.
Sources
Checked on 26 October 2026.
- FEFCO and ESBO, International Fibreboard Case Code (11th edition): https://www.fefco.org/sites/default/files/documents/FEFCO_Codes_of_Designs.pdf
- ISO 3037:2022, Corrugated fibreboard, Determination of edgewise crush resistance (non-waxed edge method): https://www.iso.org/standard/80310.html
- ISO 2248:1985, Packaging, Complete, filled transport packages, Vertical impact test by dropping (confirmed in 2022): https://www.iso.org/standard/7062.html
- International Safe Transit Association, test procedures: https://ista.org/test_procedures.php
- ASTM D4169-23e1, Standard Practice for Performance Testing of Shipping Containers and Systems: https://store.astm.org/d4169-23e01.html
- ASTM D642, Standard Test Method for Determining Compressive Resistance of Shipping Containers, Components, and Unit Loads: https://store.astm.org/d0642-20.html
- Regulation (EU) 2025/40 on packaging and packaging waste, Article 24 and the application date: https://eur-lex.europa.eu/eli/reg/2025/40/oj/eng
- Japan Customs, Japan’s Tariff Schedule as of 8 August 2026, Chapter 48: https://www.customs.go.jp/english/tariff/2026_08_08/data/e_48.htm