Mailing bags vs boxes: which is best for posting your products?

Use a mailing bag for soft, unbreakable items such as clothing, textiles and printed goods, and use a cardboard box for anything fragile, rigid, heavy or oddly shaped. Bags are lighter and flatter, which keeps postage weight down and can keep a slim item inside the cheaper Large Letter size, while boxes give crush protection that a bag never can. Whichever you choose, weighing and franking each item on a franking machine with built-in scales means you pay the right postage every time.

What is the difference between a mailing bag and a box?

A mailing bag is a flexible envelope-style pouch, usually with a peel-and-seal strip. Common types include paper mailing bags, plant-based eco mailing bags and padded mailers. They wrap closely around the item, so they add very little size or weight.

A postal box is a rigid corrugated cardboard carton. The fluted board resists crushing, holds its shape when stacked and lets you add void fill around the contents. Our guide to single wall vs double wall boxes explains how box strength varies.

The simple test is this: if the item would be damaged by being squeezed, bent or dropped, it needs a box. If it would not, a bag is usually the smarter, lighter choice.

Mailing bags vs boxes at a glance

When should you use a mailing bag?

Mailing bags are the natural choice when the item can look after itself. Choose a bag when:

• The product is soft and will not break, such as clothing, scarves, bedding or fabric.
• It is flat or flexible, such as printed matter, patterns or soft-bound items.
• You want to keep the weight and thickness as low as possible to stay in a cheaper size band.
• You send a high volume of similar items and want fast packing with no tape.

Paper bags are a popular plastic-free option. Our paper mailing bags come in standard duty (1 ply) and heavy duty (2 ply) in a range of sizes. If you prefer a plant-based alternative to conventional polythene, take a look at our sugar cane eco mailing bags.

For small items that need a little cushioning but not a full box, such as accessories or small boxed gifts, paper padded envelopes sit neatly between the two.

When should you use a box?

A box earns its place whenever damage is a risk. Choose a box when:

• The item is fragile, such as glass, ceramics, candles or electronics.
• It is rigid or has corners that could tear through a bag.
• It is heavy, or you are sending several items together.
• It contains liquids or cosmetics that must stay upright and protected.
• Presentation matters, such as gifts or premium products.

Our Royal Mail Small Parcel size boxes are made to fit inside the Small Parcel limit of 45 x 35 x 16cm and 2kg, so you get protection without accidentally tipping into the Medium Parcel band.

How your packaging choice affects postage

Royal Mail prices mail by size format and weight, and your packaging counts towards both. That makes the bag or box decision a postage decision too.

• Large Letter: up to 35.3 x 25 x 2.5cm and 750g.
• Small Parcel: up to 45 x 35 x 16cm and 2kg.
• Medium Parcel: up to 61 x 46 x 46cm and 20kg.

These limits are set out on Royal Mail’s UK sending guide. A thin T-shirt in a mailing bag can often stay under 2.5cm thick and go as a Large Letter, which is usually cheaper than a Small Parcel. The same T-shirt in a standard box would almost always be a parcel. If you want the protection of a box but the price of a Large Letter, our Large Letter size boxes are designed to stay within the 2.5cm depth.

The catch is that bags flex. An overstuffed bag can bulge past 2.5cm, and that turns a Large Letter into a parcel. Our Large Letter vs Small Parcel size guide explains where the lines fall, and our article on measuring your mail to avoid surcharges shows how to check before you post.

Why franking makes either choice easier

Getting the packaging right is only half the job. The other half is paying the right postage for the size and weight you end up with, and that is where a franking machine helps most.

• Built-in weighing: place the packed bag or box on the scale and the machine selects the correct weight step, so a light mailing bag is charged as a light item.
• One system for everything: letters, Large Letters and parcels all go through the same machine, whether they are bagged or boxed.
• Labels for any packaging: print the postage onto a franking label and stick it on a bag or box in seconds.
• Lower postage: Royal Mail describes franking as cheaper than stamps, so every bag and box you send costs less.
• Tracked and secure options: add Signed For or Special Delivery for valuable boxed items.
• No queues: pack, weigh, frank and hand over, without a trip to the Post Office counter.

Find out more about our franking machines and how they fit a busy packing bench.

How to choose between a bag and a box in 4 steps

1. Check how fragile the item is. If squeezing, bending or dropping it could cause damage, choose a box.
2. Measure the item. If it is soft and flat enough to stay under 2.5cm thick, a mailing bag could keep it in the Large Letter band.
3. Pick the smallest packaging that protects it. Extra space adds weight and lets items move, so match the bag or box closely to the item.
4. Weigh and frank the packed item. Put it on your franking machine scale, check it is within the Royal Mail size and weight limits, and print the exact postage.

Are mailing bags and boxes recyclable?

Paper mailing bags and corrugated cardboard boxes are both paper-based, so customers can usually recycle them with their paper and card once labels and tape are removed where possible. Sugar cane eco mailing bags are made using a plant-based material rather than oil-based polythene. Visit our packaging supplies page to see our eco-friendly ranges.

Need help?

Not sure whether your products should go in a bag or a box, or how a franking machine could cut your postage? Our team is happy to help. Call Mailcoms on 01543 572 776 or explore our full range of packaging supplies.

Frequently asked questions

Can I post clothes in a mailing bag?

Yes. Clothing is one of the best uses for a mailing bag because it is soft, will not break and packs flat. A paper or eco mailing bag keeps the weight low, and a thin garment may even fit the Royal Mail Large Letter size.

Is it cheaper to send a parcel in a bag or a box?

A bag is often cheaper to post because it weighs less and can keep a slim item under 2.5cm thick, which may let it go as a Large Letter instead of a Small Parcel. Weighing it on a franking machine makes sure you pay the exact postage for its size and weight.

Does Royal Mail accept mailing bags?

Yes. Royal Mail prices mail by size and weight rather than packaging type, so a mailing bag is fine as long as it is securely sealed and stays within the limits for its size format.

When should I use a box instead of a mailing bag?

Use a box for anything fragile, rigid, heavy, liquid or valuable, or anything that could be crushed or tear through a bag. The rigid cardboard and void fill protect the contents in a way a bag cannot.

Can I put a franking label on a mailing bag?

Yes. Print the postage onto a franking label and stick it on a flat, smooth area of the bag, away from the seal and any creases, so it can be read clearly.

Are paper mailing bags strong enough for posting?

For soft, non-fragile items, yes. Heavy duty 2 ply paper mailing bags offer extra strength for heavier or bulkier goods, but anything breakable should still go in a box.