Choose a postal format by carrier band first, then by protection. Letterbox-depth packs avoid a failed delivery entirely, which is worth more than the mailer costs. Beyond that the choice is between mailers for compressible goods, book wraps for flat items and boxes for anything rigid.
Why the band matters more than the material
Parcel carriers price on bands of size and weight, and they apply volumetric rules - so the air inside an oversized pack is charged as though it were goods. A format that sits just inside a threshold costs materially less to send than one just outside it, and that difference repeats on every despatch.
The threshold worth checking first is letterbox depth. A pack thin enough to go through a door avoids a delivery attempt, a card and a redelivery - and those cost far more than any mailer. For small flat items it is frequently the single largest saving available.
| Format | Suits | Watch out for |
|---|---|---|
| Letterbox carton | Small flat items, high delivery-attempt cost | Depth limit is strict - measure, do not estimate |
| Padded or bubble mailer | Small robust items | Puncture; little crush resistance |
| Paper padded mailer | Brand-led sellers wanting kerbside recycling | Wet weather handling, slightly higher cost |
| Polythene mailer | Compressible goods, apparel | No protection; no presentation |
| Book wrap | Books, flat printed matter, framed items | Sized to the item or it loses its advantage |
| Postal box | Rigid or fragile items | Oversizing; fill becomes necessary |
| Tube | Rolled prints, posters, long thin items | Crushed ends without caps |
Postal formats and what each is for.
Parcels fail differently from pallets
A pallet is handled twice by machinery. A parcel is handled many times by people and conveyors, sorted on its corners, dropped from belt height and stacked under whatever follows it. Packaging leaving on a parcel network has to survive handling it will definitely receive rather than the careful handling it ideally would.
That changes what protection means. Corner and edge strength matter more than overall rigidity; a pack that cannot be crushed flat matters more than one that looks substantial. And anything that can move inside the pack will move, repeatedly, for the whole journey.
Choosing between a mailer and a box
- Compressible and robust - a mailer, almost always. A box around soft goods is paying for volume that does nothing.
- Flat and rigid - a book wrap sized to the item beats both, because it fits the product rather than approximating it.
- Rigid and fragile - a box, right-sized, with protection chosen against the failure mode rather than by default.
- Awkward or projecting - a box with a fitted insert; a mailer will tear at the projection.
- High value or brand-led - a box or a printed mailer, because the outer is the customer's first physical contact.
The commonest ecommerce packaging error is a single box size used for everything. It guarantees that most despatches ship air, need fill, and sit a band higher than they should - see ecommerce packaging.
Returns are part of the format decision
On any line with a meaningful return rate, the pack the customer cannot reseal is a pack that guarantees the product comes back in something worse. A resealable closure on a mailer, or a supplied returns pack, costs very little against the cost of a product returned damaged and unsellable.
It is worth deciding this at specification rather than retro-fitting it after customers have improvised. See returns management for how the return leg is handled once it reaches us.
Building a postal range from the order profile
The range should come out of what your orders actually contain, not out of the product catalogue. Those are different documents and only one of them describes what leaves the bench.
- Take a month of real orders, not a representative sample chosen by hand.
- Sort them by what they contain - single small item, single large item, multi-item, and the awkward exceptions.
- Find the proportions. In most ecommerce operations a small number of order shapes cover the large majority of despatches.
- Specify a format for each of the major shapes, and one fallback for the exceptions.
- Check each against the carrier bands before committing - a format that sits just over a threshold undoes its own advantage.
| Order shape | Share of despatches | Format |
|---|---|---|
| Single small flat item | Often the largest group | Letterbox pack |
| Single small rigid item | Substantial | Small postal box |
| Two or three items | Moderate | Mid postal box |
| Large or heavy | Small | Double wall box |
| Awkward or fragile | Few | Box plus fitted protection |
A typical outcome of that exercise.
Four or five formats chosen this way usually outperform both a single universal box and a deep ladder nobody can pick from quickly.
The short version
- Check the carrier band before the material; it is where the money is.
- Letterbox depth avoids a failed delivery, which outweighs the mailer cost.
- Parcels are handled many times, so corner strength beats general rigidity.
- Compressible goods belong in a mailer; rigid and fragile in a right-sized box.
- Specify the return pack at the same time on any high-return line.
Frequently asked questions
What is the cheapest way to send a small item?
Usually a letterbox-depth pack, provided the item genuinely fits. It avoids a delivery attempt and a redelivery, and those cost far more than the difference between any two mailers.
Are padded mailers enough protection?
For small robust items, often yes. They offer very little crush resistance and can be punctured on a mixed parcel, so anything rigid, fragile or projecting is better in a right-sized box.
Paper or plastic mailers?
Paper goes into household kerbside recycling and reads better to most customers; plastic is lighter, cheaper and handles wet weather better. Both work - see sustainable packaging.
How many postal sizes should we carry?
Enough that a typical order fits closely and few enough that a packer chooses correctly under pressure. Build the range from the order profile rather than the product catalogue.
Do book wraps only suit books?
No - they suit anything flat and rigid, including framed items, printed matter and boxed flat goods. They fit the product rather than approximating it, which is why they usually sit in a lower band than a box would.