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Use a poly mailer for soft, unbreakable goods like clothing: it weighs almost nothing, costs less to ship, and shrugs off rain. Use a box for anything rigid, crushable, or fragile. The deciding question is not weight but shape: if the item can be bent, folded, or crushed without damage, it belongs in a mailer.
| Poly mailer | Cardboard box | |
|---|---|---|
| Best for | T-shirts, hoodies, fabric, soft toys, padded items | Anything rigid, heavy, fragile, or oddly shaped |
| Packaging weight | A few grams; barely registers on the scale | Several hundred grams for a medium box |
| Crush protection | None: the mailer conforms to whatever is under it | Good: the box takes the load, not the contents |
| Water resistance | Excellent: plastic sheds rain | Poor unless you add a plastic liner |
| Puncture risk | Higher: sharp edges can poke through | Lower |
Two reasons, and only one is the packaging weight. The obvious one: a mailer weighs almost nothing, so you pay for the item's weight and nothing more. The subtler one is dimensional weight: carriers charge by whichever is greater, actual weight or the space the parcel takes up, and a mailer hugs the item while a box adds inches of air on every side. A hoodie in a mailer can bill at a fraction of the same hoodie in a box because the mailer eliminates the empty space.
This is also why the mailer has to fit. An oversized mailer with a small item inside bunches up, slides around, and can actually bill worse than a snug box. Buy mailers in a couple of sizes and match the item: the mailer should be just large enough to seal with an inch or two of slack.
Anything that cannot survive being stepped on. That sounds dramatic, but parcels get stacked, and a mailer transmits every pound above it straight to the contents. The never-list: framed photos or artwork (glass and frames crack), books you care about (corners crush), anything with a screen, ceramics, candles in warm weather, and liquids of any kind. A bottle of hot sauce in a mailer is a disaster for everyone whose parcel rides below it.
The grey zone is semi-rigid goods: board games, vinyl records, thin electronics accessories. These can travel in a mailer only with rigid reinforcement, a stiff cardboard insert on each side that turns the mailer into a sandwich. Bubble mailers (padded envelopes) split the difference for small, sturdy items like phone cases or cosmetics: some puncture protection, still lightweight, still no crush protection. When in doubt, the box is the safe answer: the small saving is not worth a damage claim.
A few that surprise people. First, customs: an opaque sealed mailer cannot be easily opened and resealed for inspection the way a taped box can, so some cross-border mailers get extra scrutiny or are opened destructively. Second, labeling: the slick plastic surface takes adhesive labels fine, but thermal labels applied in a cold warehouse can peel; press the label flat and smooth out air bubbles. Third, returns: a torn-open mailer is harder to reuse than a box, which matters if you ship to customers who might send things back.
There is also an environmental angle worth knowing. Poly mailers are plastic film, and most curbside recycling programs do not accept them; they belong in store drop-off film recycling where it exists. If sustainability matters to your customers, paper-based padded mailers exist, though they cost more and protect less against rain.
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