What is an SOS Bag? (Self-Opening Sack)

An SOS bag is a flat-bottomed paper bag with pleated side gussets and no handles, made so it springs open and stands up on its own when you flick it. SOS stands for self-opening sack. In Australia it is the standard brown kraft bakery, grocery, deli and takeaway bag, sold in numbered sizes.

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What SOS stands for, and why the design exists

Self-opening sack describes what the bag does rather than what it is made from. Hold a stack of SOS bags in one hand, flick the top one, and it opens and holds its shape without being pulled apart with two hands. That single-handed action is the reason the format has survived unchanged for over a century.

Think about the job it was invented for. A counter hand is holding tongs, a pie or a customer's change. If the bag needs two hands to open, every order slows down. The SOS bag was designed so the bag opens in the hand that is already holding it, and stands on the bench while the other hand fills it.

How the flat bottom and side gussets work

Two features do the work. The bottom is a folded and glued block, not a seam across the base, so when the bag opens the base flattens into a rectangle that sits square on a bench. The sides are pleated inwards as a gusset, which lets the bag lie flat for storage and then expand to a set depth when opened.

The gusset is the third dimension of the bag. A 160 x 300mm bag with an 85mm gusset opens to a base roughly 85mm deep, which is why two bags with identical width and height can hold very different amounts. Gusset depth is the number to check when you are matching a bag to a bulky item rather than a flat one.

SOS, flat, gusseted and twist handle paper bags

Four paper bag formats sit next to each other on most counters and only one of them stands up on its own.

Bag type	Handles	Bottom	Stands up on its own	Typical use
SOS bag (self-opening sack)	None	Flat glued block bottom	Yes	Bakery, grocery, deli, takeaway, market stalls
Flat paper bag	None	Flat seam, no gusset at all	No	Sandwiches, lollies, tuckshop orders, single items
Gusseted flat bag	None	Flat seam with side gussets only	No, it expands but will not stand	Pies, pastries, bread, bulkier single items
Twist handle carry bag	Twisted paper handles	Flat block bottom with side gussets	Yes	Retail, takeaway meals carried out by hand

The practical dividing line is whether the bag needs to be carried any distance. An SOS bag is a counter bag: filled fast, handed over, carried a short way or dropped into something else. Once a customer has to walk with it, a twist handle carry bag is the better choice.

How SOS bag sizes are described in Australia

Australian suppliers quote paper bags as a numbered size backed by measurements in millimetres. QIS quotes width by height, with the gusset stated separately, because the gusset applies to both the sides and the bottom. Some suppliers write the same bag as width x gusset x height, so always confirm which of the three numbers is the gusset before you compare two quotes.

Size	Width x height	Gusset	Suits
Size 1	120 x 210mm	60mm	Single pastries, small goods, pharmacy items
Size 2	130 x 260mm	80mm	Rolls, buns, small deli orders
Size 3	160 x 300mm	85mm	Bread, mixed bakery orders, greengrocer items
Size 4	240 x 390mm	120mm	Grocery orders, larger takeaway
Size 5	340 x 430mm	175mm	Full grocery loads, bulky produce
Size 25	360 x 540mm	165mm	Tall items, large market and grocery orders

Paper weight is the other half of the specification, and in Australia it is quoted in gsm, grams per square metre. A heavier sheet carries more weight and copes better with anything damp or greasy, while a lighter sheet is fine for a single bun and costs less to hold in volume. Check the stated gsm on the bag you are considering rather than assuming, because two bags of identical dimensions can be made from very different paper.

SOS bags in Australia

The single most useful thing to know here is that SOS bags sit outside every state and territory plastic shopping bag ban. Those bans cover plastic bags, and in most jurisdictions specifically plastic carry bags with handles. NSW, Victoria, Tasmania and Queensland ban lightweight plastic shopping bags with handles at or under 35 microns, Western Australia bans all plastic shopping bags with handles regardless of thickness, South Australia bans plastic film shopping bags that are not certified compostable, and the ACT has banned both lightweight and heavyweight plastic carry bags. A paper bag with no handles is not caught by any of them.

That regulatory certainty is a large part of why Australian bakeries, greengrocers, delis and takeaway shops moved to SOS bags rather than to a thicker plastic bag. The format has not had to be redesigned once as each state changed its rules, which matters when you are holding stock.

Two more local notes. Australian numbered sizes are a supplier convention rather than a standard, so a size 3 from one supplier will not always match a size 3 from another, and the millimetre measurements are what you should compare. And if you are wrapping food inside the bag as well, remember the packaging obligation comes from the FSANZ Food Standards Code: Standard 3.2.2 requires packaging to be fit for its intended use and not likely to cause food contamination. QIS holds the full SOS range in Brisbane, despatches same day on orders placed before 12pm and ships Australia-wide, on 1800 555 343.

Related guides

The gusset is the feature that makes this bag work, so what is a gusset is the place to start. The material is covered in what is kraft paper, and paper weight in what is gsm. For the reusable bag that sits alongside these at the counter, see what is NWPP.

Sizes, pack quantities and stock levels for the whole range sit on the paper bags page.

Not sure which size and gusset suits your counter? Contact our Brisbane team.