A flat kraft mailer holds its shape. A gusseted one is built to change shape, expanding at the base or the sides to take a bulkier or more irregularly shaped order without needing a second, larger mailer size on the shelf. This guide covers how a gusset actually works, when it earns its place in your packaging range, and what to check before ordering a custom gusseted run.
What a gusset actually is
A gusset is a folded panel built into the base or sides of the mailer that stays flat when empty and expands outward when the mailer is filled, similar in principle to the folded base of a paper shopping bag. On a kraft mailer it usually appears as a bottom gusset, adding depth to the parcel, though side gussets exist for wider, flatter loads. The gusset depth, commonly in the range of 40mm to 120mm depending on the mailer size, sets how much extra volume the mailer can absorb before it is genuinely full.
Why a gusset matters more than it looks like it should
Without a gusset, a kraft mailer is essentially a flat envelope, it holds a flat or thin item well and copes poorly with anything that has real depth. Force a bulky, multi-item, or oddly shaped order into a non-gusseted mailer and the seal is put under strain at exactly the point it needs to hold, the corners stretch, and the mailer can split along a seam under normal handling. A gusset solves this by giving the parcel somewhere to actually put that extra depth, rather than asking the flat panels of the mailer to stretch to accommodate it.
When to specify a gusseted mailer
- Multi-item orders where the combined depth of several products exceeds what a flat mailer can hold without strain.
- Bulkier single items, folded apparel with some thickness, boxed small goods, anything with real volume rather than being genuinely flat.
- Order volume that varies, where a single gusseted size flexes to cover a range of order sizes that would otherwise need two or three separate flat mailer sizes.
- Products moving from a carton to a mailer to cut cost and material, where the gusset is what makes that switch possible without losing the volume the carton was providing.
When a flat mailer is still the better choice
If your product is genuinely thin and consistent in size, documents, prints, single flat garments, a gusset adds cost and unused capacity for no benefit. Reserve gusseted stock for the part of your order range that actually varies in bulk, and keep a flat or plain kraft mailer for the part that does not, running one gusseted format for everything usually means overpaying on your simplest orders.
How much gusset depth do you actually need
| Order type | Typical gusset depth |
|---|---|
| Single folded garment or light multi-item order | Around 40 to 50mm |
| Standard multi-item ecommerce order | Around 60 to 80mm |
| Bulkier orders, small home goods, layered apparel | 100mm or more |
As with any mailer, resist the urge to size up “to be safe.” A gusset that is deeper than the order needs leaves the parcel under-filled and loose inside a mailer that can still bend or crush at that empty depth, right-sizing the gusset matters as much as right-sizing the mailer’s length and width.
Cost impact of moving to a gusseted mailer
A gusseted mailer uses more kraft paper than a flat one of the same width and length, so the per-unit material cost is slightly higher. Where it usually pays for itself is on the freight side: if a business is currently using a small carton to get the depth a gusseted mailer could provide instead, the switch typically reduces both material weight and, because carriers bill on the greater of actual and dimensional weight, the freight cost per parcel. The comparison worth running before committing to a gusseted range is not gusseted mailer versus flat mailer, it is gusseted mailer versus whatever bulkier format you are using today for the same orders.
Who relies on gusseted kraft mailers
Demand for this format clusters around a few order profiles: multi-item ecommerce brands where the combined order depth varies week to week, apparel and homewares businesses shipping folded, layered or slightly bulky product, and any business currently over-using cartons for orders that do not actually need a rigid box, just more depth than a flat mailer offers. If your order profile is consistently thin and single-item, a gusseted range is unlikely to be worth adding.
Closure on a gusseted mailer
The base or side gusset does not change how the mailer closes at the top, a self-seal strip works the same way it does on a flat mailer, and a tear-strip opening can be added the same way too. The one practical difference is fill: pack the order fully into the gusset before sealing, an under-filled gusseted mailer folds unpredictably and can look poorly packed even when the contents are perfectly protected.
Padding and gussets together
A gusset adds volume; it does not add cushioning. For bulkier orders that also need impact protection, pair a gusseted base with a padded lining, honeycomb for a fully paper result or bubble-lined where maximum cushioning matters more, rather than assuming extra depth alone equals extra protection.
A simple way to check if your gusset size is right
- Pack a real order into the mailer the way it will actually be packed day to day, not a best-case single item.
- Check the gusset folds flat against the base once sealed, rather than staying puffed open, a gusset that will not close flat is oversized for that order.
- Check the seal is not under visible strain at the corners or along the top edge, strain here means the gusset is undersized for the order and the mailer is being forced to stretch.
- Repeat with your smallest and largest typical orders, not just an average one, since a gusset that works for the average may fail at either end of your real order range.
If most orders sit clearly on one side of that test, either mostly under-filling the gusset or mostly straining it, that is a sign to adjust the gusset depth rather than accept either outcome as normal.
How Carewell Group helps
Carewell Group is an Australian packaging manufacturer and supplier. We specify gusset depth to your actual order profile rather than a single generic depth across your whole range, and can combine a gusset with padding, closure type and custom branding in the one mailer. See the full kraft paper mailer types and ordering guide for how gusseted mailers fit alongside flat and padded formats.
Carewell can meet all your packaging needs for your business. Talk to our expert and we will work to your required MOQ. Call +61 (02) 8760 1491 or request samples and a packaging review.
Branding on a gusseted mailer
Print placement needs slightly more thought on a gusseted mailer than a flat one, since the gusset panel folds and stretches with the fill level, a design element printed across that panel can look different depending on how full the order is. Keep primary branding, logo and colour, on the flat front and back panels, and use the gusset itself for secondary detail like a care instruction or a batch code that reads fine whether the gusset is fully or partially expanded. See custom-printed kraft mailers for the general print guidance this builds on.
Frequently asked questions
What is a gusseted kraft mailer?
A mailer with a folded panel built into the base or sides that expands to hold bulkier or multi-item orders, rather than staying completely flat like a standard mailer.
How deep should the gusset be?
Match it to your actual order profile, roughly 40 to 50mm for light multi-item orders, 60 to 80mm for standard ecommerce orders, and 100mm or more for bulkier goods. Avoid oversizing, an under-filled gusset can fold or crush unpredictably.
Do I need a gusset if my orders are always the same size?
No, a flat or plain kraft mailer is the more cost-effective choice for consistent, thin orders. Reserve gusseted stock for the part of your range that genuinely varies in bulk.
Can a gusseted mailer also be padded?
Yes, a gusset adds volume and a padded lining adds cushioning, they solve different problems and can be combined in one mailer where the order needs both.
Is a gusseted mailer cheaper than a small carton?
Often, once freight is included. Carriers bill on the greater of actual and dimensional weight, so switching a bulky order from a carton to a right-sized gusseted mailer, where the product allows it, typically reduces both material weight and freight cost per parcel.
Should I use one gusseted size for my whole product range?
No, run a gusseted format for the part of your range that genuinely varies in bulk and keep a flat or plain mailer for consistently thin orders, using one deep gusset for everything overpays on your simplest parcels.
Sources
- Australia Post, parcel size and packaging guidelines: auspost.com.au
Written by Alif Vasaya, digital and content strategy, Carewell Group. Carewell Group is an Australian packaging, food packaging, tape, industrial safety and 3PL supplier serving all of Australia. Last updated 17 September 2026.