Postage Bags in Australia | The Complete Guide to Choosing the Right Mailer

BagMasters Team · Last updated 22 September 2026 · 11 min read

The short answer: choosing the right postage bag in Australia comes down to what you are sending. Use a tough, opaque poly satchel for clothing, textiles and soft goods. Use a padded (bubble-lined) mailer for books, cosmetics, electronics accessories and anything that can crack or dent. Size the bag to the item, check the film is opaque and the seal is tamper-evident, and buy by the carton to bring the cost per bag down.

BagMasters has been making and supplying commercial bags from Melbourne since 1983, and postage bags are one of the questions we answer most. This guide walks through the main types of mailing bags in Australia, how to pick a size, what thickness and opacity actually mean, when custom printing is worth it, and how carton buying changes your cost per unit.

What are postage bags?

Postage bags (also called postal bags, post bags, mailing bags or mailer bags) are flat, self-sealing bags designed to carry goods through Australia Post or a courier network without a box. They are lighter than cartons, take up less room on your packing bench, and often cost less to send because the parcel is smaller.

You will also hear the word satchel. In the packaging trade a satchel is simply a flat mailing bag, usually polyethylene, with a fold-over flap. Australia Post sells prepaid satchels, but many businesses buy plain or branded satchels in bulk and pay postage separately through their carrier account.

The main types of postage bags in Australia

Most online sellers and mailrooms use a mix of three or four bag types. Here is how they compare.

Poly satchels

A good poly satchel is the workhorse of e-commerce. Look for multi-layer film rather than a single thin layer: co-extruded (layered) polyethylene is tougher to tear and puncture for the same weight. Our Jet Black BagMasters Satchels are made from three-layer, high-impact black polyethylene that is 100% opaque, with a permanent peel-and-seal closure.

Padded and bubble mailers

Padded mailers bond a layer of bubble cushioning inside the outer film. They are the step up when a satchel would leave an item exposed to knocks but a box would be overkill. Choose between end-opening styles (load from the short edge, good for long, slim items) and side-opening styles (load from the long edge, easier for books, packets and wider flat items).

Reusable courier bags

If your "postage" is really internal mail moving between sites, a reusable fabric courier bag is often better value than throwing away single-use satchels every day. BagMasters manufactures these in Melbourne, including lockable and custom-branded versions. See our custom bag options.

How to choose the right postage bag: a quick decision guide

Work through these questions in order. Most people have their answer by step three.

1. Can the item break, crack, dent or scratch?
   Yes: go to a padded mailer (or a box for anything heavy or very fragile). No: a poly satchel will usually do the job.
2. Is it flat and wide (a book, a packet, a folded garment) or long and slim?
   Wide and flat: side-opening padded mailer or a satchel. Long and slim: end-opening mailer.
3. Do the contents need to stay private?
   Yes: choose a 100% opaque bag (black film or a black padded mailer) so nothing can be read or seen through the bag.
4. Do you need to show if a parcel has been opened?
   Yes: use a permanent, tamper-evident seal. The bag cannot be opened and resealed without visible damage.
5. Is it going between your own sites, again and again?
   Yes: consider a reusable courier bag instead of single-use satchels.
6. Do you post more than a few hundred parcels a month?
   Yes: buy by the carton, and consider custom printing once volumes justify it.

Postage bag sizes: how to get the fit right

Postage bag sizes are quoted as width × depth (or length) + flap, in millimetres. The width is the opening edge; the depth runs from the opening to the bottom seam. The flap is extra and folds over to seal.

To choose a size:

• Measure the item's width and length, and its thickness.
• Add the thickness to both the width and the length. A 30 mm thick item uses up about 30 mm of each dimension once it is inside the bag.
• Leave another 10–20 mm so the item slides in and the flap seals flat without strain.
• For padded mailers, allow a little more: the bubble lining takes up some internal space.

Here are the sizes of our stock Jet Black satchels, taken from the product listing:

Check carrier limits. Australia Post's domestic limits are currently 22 kg, 105 cm maximum length and 0.25 cubic metres, and courier companies set their own. Always check your carrier's current size and weight guidelines before you settle on a bag size.

Thickness, strength and opacity

What does micron mean?

Plastic film thickness is measured in microns (one micron is one-thousandth of a millimetre). Thicker film is generally stronger, but construction matters too: a multi-layer co-extruded film can outperform a thicker single layer. When comparing postage bags, ask about the film construction as well as the micron rating, and test a sample with your heaviest or sharpest item.

Why opacity matters

A thin, light-coloured bag can show printing, packaging or even the item itself through the film. That is a privacy problem for medical, personal and high-value goods, and it can make a parcel a target for theft. A fully opaque bag, such as a jet black satchel or a matte black padded mailer, blocks the view completely.

Tamper-evident seals

A permanent peel-and-seal strip bonds so firmly that the bag cannot be opened without tearing it. That gives you and your customer a simple check on arrival: if the seal is intact, the parcel has not been opened in transit. For higher-security items such as cash, documents or evidence, look at dedicated tamper-evident security bags with numbered seals.

Our top three postage bags

These three cover most of what Australian online sellers post. All are sold by the carton, with volume pricing on the product page.

Need something else? Browse the full range of postage bags and mailing satchels, including white side-opening padded mailers, plastic mail bags, banner mailers and satchel liners.

Custom printed postage bags

Printing your logo on every satchel turns each delivery into a small piece of advertising and makes your parcels easy to recognise on a doorstep. It also looks more professional than a plain bag with a sticker.

What to know before you order custom mailing bags:

• Minimums: custom manufactured satchels start from 1,000 units. Stock satchels are available from 500.
• Artwork: supply your logo as an .eps or .pdf file.
• Lead times: about 3–4 weeks for Australian-made runs, or 8–12 weeks from an overseas factory for high-volume or lower-cost orders.
• Samples: custom samples are available for $200 +GST.

Because BagMasters manufactures in Melbourne and also imports, we can advise which route suits your volume and deadline. Start on our customise page.

What do postage bags cost? Buying by the carton

Postage bags are almost always cheaper per unit when you buy by the carton, and cheaper again at higher volumes. When comparing suppliers, work out the cost per bag rather than the carton price, because carton quantities vary a lot between sizes and bag types.

Cost per bag = carton price ÷ bags per carton. Current carton prices and volume discounts are shown on each product page. Remember the bag is only part of the cost: a lighter, smaller parcel can also reduce what you pay in postage.

Common postage bag mistakes to avoid

• Using a satchel for fragile items. Poly film keeps water out but does nothing to absorb a drop.
• Choosing a bag that is too small. An over-stuffed satchel strains the seams and the seal.
• Choosing a bag that is too big. Excess film snags in sorting machines and can push you into a higher size band.
• Using see-through film for private items. Pick a fully opaque bag.
• Running out. Keep at least a few weeks of stock on hand, especially before peak season.

How BagMasters can help

We supply stock postage bags by the carton, dispatched from our Melbourne warehouse (usually within 2 business days), and we manufacture custom bags to your size and artwork. Consumable samples are free, so you can test a bag with your products before you commit. Start with the Jet Black satchels for soft goods, or the black side-opening padded mailer for anything that needs cushioning.

Postage bags: frequently asked questions