01What a mailer box is
A mailer is a die-cut corrugated box. A die cuts the outline, slots and tabs from one sheet of board. You fold the bottom panel up into the walls, fold the side walls in and lock them with tabs, then close the hinged lid and tuck its front flap inside. Unlike a shipping box, there is no glued or taped side seam, and the lid can be opened and closed again.
In the FEFCO Code, the international catalog of corrugated box designs, one-piece folding mailers sit in the 04 group, "folder boxes and trays": usually one piece of board, with the bottom hinged to form the side walls and the cover. If a supplier quotes a FEFCO number, such as 0427, ask for the drawing so you both mean the same box.
A mailer is not a folding carton (single-layer paperboard) or a rigid box (thick greyboard, glued into shape). See box styles for other forms.
02Mailer box vs shipping box (RSC)
The plain brown shipping box is the regular slotted container (RSC), which the Packaging Corporation of America calls the most common box style: all four flaps on each end are the same length, and the outer flaps are half the box width so they meet in the middle. It arrives flat with its side seam joined, and you tape it shut.
| Mailer box | Shipping box (RSC) | |
|---|---|---|
| Made from | One die-cut piece, no joint | One slotted piece with a glued, stitched or taped joint |
| Closing | Hinged lid tucks in; tape or a seal optional | Flaps meet in the center; taped shut |
| Look | Clean outside, room to print inside | Utility; center seam and tape show |
| Suits | DTC orders, subscription and PR boxes, small to mid-size products | Heavier orders, multiple items, master cartons, outer shippers |
Decision rule: if the box is part of the brand experience and the order is a known, fixed size, use a mailer. If order sizes vary, the box is heavy, or nobody sees it (a master carton or an outer shipper), use an RSC.
03Board and flute
Single wall board is two sheets of linerboard with one fluted medium between them; double wall adds a second medium and a third liner. The common flutes run from A, the tallest at about 4.8 mm, down to F at about 0.8 mm, according to the Packaging Corporation of America. A thinner flute makes thinner board and a taller one thicker board. Ask which flute the supplier proposes, how the alternative changes print and stiffness, and test both with your heaviest order.
Strength is quoted as an edge crush (ECT) or burst grade. The PCA glossary describes ECT as a predictor of a finished box’s compression strength, and notes that a box maker’s certificate is only needed when shipping by common carrier. See ECT and burst strength, and test the packed box (our ISTA testing entry covers standard transit tests).
04Kraft or white, and how to print it
The outer liner is either brown kraft paper or a white top liner. Ink sits over the brown, so colors on kraft look more muted and warmer than on white paper; a white liner prints truer. One option is brown outside with one color and white inside with full color, or the reverse. Ask for a printed sample on the actual board before bulk.
| Method | How it works | What PCA says it suits |
|---|---|---|
| Direct flexo (post-print) | Ink printed straight onto the liner of the finished board | Low to medium resolution; any quantity |
| Direct digital | Inkjet straight onto the board | Medium resolution; small quantities |
| Flexo preprint | Liner printed on the roll before it becomes board | Medium to high resolution; high volumes |
| Litho lamination | Sheet printed offset, then laminated onto the board | High-quality graphics; a wide range of quantities |
For a small first order, PCA’s guide points to direct digital, while direct flexo works at any quantity; if your supplier runs both, get both quoted. Ask for inside print as a separate line. Finishes and color matching are in printing methods and Pantone vs CMYK.
05Inserts and void fill
Size the mailer to the product first. Where the product would still move, add an insert (die-cut corrugated or paperboard, molded pulp, or foam for fragile goods); where it only rattles, use void fill such as crumpled kraft paper. FedEx’s packing guide says to fill empty space so goods cannot move inside the box during shipping.
06Ship it as-is or inside a shipper
A corrugated mailer can be the outer box. FedEx’s US packing guide says you may use your own packaging if boxes are sturdy and undamaged with all flaps intact, while chipboard boxes such as gift or shoe boxes must go in a corrugated outer box. The same guide says items that could be damaged by normal handling, including marking or adhesive labels, belong in a protective outer box.
- Ship as-is when a scuff or a shipping label on the print is acceptable. You pay for one box and the smallest parcel.
- Put it in a plain shipper when the box is a gift, a retail-ready box or a PR kit that has to arrive clean. You pay for a second box and a bigger, heavier parcel.
07Dimensional weight
Carriers charge for space as well as weight. FedEx calculates dimensional weight by multiplying length, width and height in inches and dividing by 139 for US shipments, and charges the greater of the dimensional weight and the actual weight. Other carriers and contracts differ; check your rate guide.
Example (illustrative numbers): a 12 x 10 x 6 inch mailer has a dimensional weight of about 5.2 lb (720 divided by 139). Cut the depth to 4 inches and it drops to about 3.5 lb (480 divided by 139). If the packed order weighs 2 lb, both are billed on dimensional weight, so the shallower box is the cheaper one to ship. These are before any rounding; check how your carrier rounds dimensions and weight.
08Mailer box or poly mailer
Poly mailers (plastic film bags with a peel-and-seal strip, sold plain or as custom poly mailers with your print) do a different job. FedEx suggests padded or poly mailers as alternatives to boxes.
| Mailer box | Poly mailer | |
|---|---|---|
| Protection | Holds its shape; resists crushing | None against crushing; a plastic layer against dirt and water |
| Size and weight | Rigid volume, so dimensional weight can apply | Flat and light; takes the shape of the contents |
| Unboxing | A lid, inside print, inserts | Tear open |
| Fits | Fragile, boxed or presentation products; gifts, kits, subscriptions | Soft goods: apparel, textiles, unbreakable items |
Before you print "recyclable" on either one, read the claim rules below; the same FTC test applies to film and to board. For paper mailers as a third option, see kraft paper.
09Recyclable claims and FSC
In the US, a "recyclable" label on a box is an environmental marketing claim under the FTC Green Guides (16 CFR 260.12). You can make an unqualified claim only when recycling facilities are available to a substantial majority, defined as at least 60%, of the consumers or communities where the item is sold, and any component that significantly limits recycling makes the claim deceptive. Check the finished box, including foam inserts, plastic windows and laminated films, not just the board. General information, not legal advice.
To print the FSC label on the box, the box maker or printer needs its own FSC chain-of-custody certificate; FSC says chain of custody is what lets an organization put its label on finished products. A brand that only sells the product generally uses FSC’s promotional license to talk about FSC in its marketing. Ask the supplier for its FSC certificate code before you pay extra for FSC board.
10How to spec it with a supplier
Two mailer quotes can differ by flute, liner and print coverage without saying so. Write these lines into your packaging spec or tech pack, with a dieline from the supplier for your size. The Vault lists packaging factories with contacts; the public list is at packaging manufacturers.
| No. | Field | What to write |
|---|---|---|
| 01 | Style | One-piece die-cut mailer with tuck front and locking tabs (or the FEFCO number and drawing) |
| 02 | Dimensions | Internal L x W x D in inches or mm, with tolerance; state internal, not external |
| 03 | Board | Single or double wall, flute, and ECT or burst grade |
| 04 | Liners | Outer and inner liner: brown kraft or white top |
| 05 | Method, number of colors, Pantone references, outside and inside coverage | |
| 06 | Insert | Material and cavity sizes, built from a physical product sample |
| 07 | Certification | FSC chain of custody (certificate code), if you plan to print the label |
| 08 | Packing | Flat boxes per bundle and per carton or pallet, carton size and weight |
Questions to ask the supplier
- Which flute and board grade do you propose for this size and weight, and what is the alternative?
- What is your minimum per size and print, and the unit price at my quantity and at double it?
- Do you need a new cutting die for my size, and is its cost a separate line?
11FAQ
Q01What is the difference between a mailer box and a shipping box?
A mailer is one die-cut piece with a hinged lid that tucks in, built to be opened like a box. A regular slotted container (RSC) has four flaps on each end that meet in the middle and get taped. Mailers suit fixed-size, presentation orders; RSCs suit heavy or varied ones.
Q02What flute are mailer boxes made from?
There is no single answer: the flute is chosen for the box size and the product weight. Ask the supplier which flute it proposes, ask how the alternative compares, and test both with your product.
Q03Are mailer boxes recyclable?
Whether you can print "recyclable" depends on the finished box, not just the board. Under the FTC Green Guides an unqualified claim needs recycling available to at least 60% of the consumers or communities where it is sold, and nothing on the box can significantly limit recycling.
Q04What is a custom mailer box?
A mailer made to your internal dimensions and printed with your design, usually with a cutting die for your size. Stock mailers come in set sizes, plain or with a sticker or stamp.