How Strong Are Grey Mailing Bags? UK Strength, Thickness & Tear-Resistance Guide 2026

Every year, UK shoppers receive dozens of parcels, and each one is handled, dropped, sorted and stacked many times before it reaches the doorstep. Industry figures suggest UK consumers receive around 75 parcels per person per year, with hundreds of parcels moving every second across the country. Strong packaging is no longer a nice-to-have – it is essential for keeping items safe, protecting margins and avoiding waste.

Grey mailing bags are the workhorse of UK eCommerce. They are used to send clothing, textiles, soft toys and thousands of other products through Royal Mail, Evri, DPD and Amazon Logistics every day. In this guide, we look at what makes a grey mailing bag truly “strong” in 2026, how thickness and microns work, how different couriers treat parcels, and how to match bag strength to your products so you can protect both your goods and your profit.

What Makes a Mailing Bag “Strong” in 2026?

A strong mailing bag does more than simply hold an item. In 2026, strength means the bag can cope with automated conveyors, cage drops, van stacking and poor weather, without splitting, leaking or popping open. True strength comes from a mix of factors working together:

• Film thickness (microns): thicker film (measured in microns) offers better tear resistance and puncture strength.
• Polymer quality: high-grade polymer blends stretch before tearing and cope better with cold and heat.
• Seal and adhesive: a long, consistent glue strip that forms a tamper-evident closure.
• Bag design: neat side welds, correctly sized flaps and consistent tolerances.
• Opacity: double or well-pigmented film that stays opaque even when the bag is full.

When all of these elements are right, your mailing bag behaves like a flexible shell around your product, not just a thin layer of plastic that can be pierced or pulled apart.

Microns Explained: The Real Difference Between 55mu and 70mu

Mailing bag thickness is usually given in microns (often written as “mu” or “µm”). One micron is one thousandth of a millimetre. The higher the micron, the thicker and heavier the film.

Typical ranges you will see in the UK are:

• 40–50mu: very light, often sold as “budget” bags. These are prone to tearing and seal failure with heavier clothing and boxes.
• 55–60mu: suitable for light clothing, soft items and low-risk parcels.
• 60–70mu: the sweet spot for serious eCommerce – strong enough for hoodies, jeans, joggers and small boxes.

The difference between 55mu and 70mu may look small on paper, but in practice it is huge. A 70mu bag resists tearing more effectively, feels sturdier in the hand and holds up better when dragged, dropped or squeezed on conveyors.

Are Grey Mailing Bags Stronger Than Coloured Mailing Bags?

Grey mailing bags have become the standard choice for UK retailers because they offer a reliable balance of strength, privacy and cost. The grey pigment helps keep the film fully opaque and can improve the overall feel of the bag.

However, colour alone does not decide strength. A 60mu grey bag and a 60mu coloured bag made from the same quality polymer will perform similarly. The key is to compare like-for-like thickness and material quality. At Mr Bags, our core Grey Mailing Bags and our coloured mailing bags ranges (including pink, purple, green and blue) use strong, consistent film so you can choose colour for branding without losing strength.

Real UK Stress Tests: How We Test Mailing Bag Strength

To judge strength properly, we look at how bags behave under real-world conditions, not just on a spec sheet. Typical tests include:

• Stretch and tear test: the bag is pulled in opposite directions to see how far it stretches before the film starts to tear.
• Corner puncture test: a boxed corner or folded jeans are pushed against the film to check for splitting.
• Drop test: packed bags are dropped repeatedly from waist height, and off a bench, to mimic delivery handling.
• Seal test: sealed bags are pulled and twisted to check whether the adhesive gives way.
• Cold and damp test: bags are stored in cooler, damp conditions before testing seals again.

From these tests, 60–70mu grey mailing bags consistently perform best for clothing and soft goods. Thin 40–50mu bags fail early, especially at the seals and around sharp corners.

Tear Resistance: How Much Pull Can a Grey Mailing Bag Take?

Tear resistance is what stops a small nick turning into a full rip. In busy networks, parcels may snag on machinery, catch on other parcels or be pulled out of cages in a hurry. A weak film tears right across; a strong film will stretch and hold together.

For clothing, we see the highest tear stress on bags containing:

• heavy denim
• bulk knitwear
• hoodies and sweatshirts
• multi-item orders

To cope with this, choose mid-size bags like 12×16 inch and 13×19 inch in a strong micron. These sizes give enough room for even folding and reduce strain on the film.

Seal Strength: Why Good Adhesive Matters for UK Couriers

Even the thickest film cannot save a parcel if the seal fails. A strong self-seal adhesive should grip quickly, hold under pressure and show if anyone has tried to open the bag. Poor adhesive is a hidden weakness that often shows up only after the first few hundred parcels go out the door.

Common seal issues include:

• flaps lifting in cold weather
• seals peeling when bags are overfilled
• adhesive sticking poorly to dusty or fibrous clothing

For heavier items, many sellers add a strip of packaging tape over the flap. This simple step greatly increases the strength of the closure and reduces the risk of open parcels arriving at the customer’s door.

Water Resistance: Can Grey Mailing Bags Survive UK Rain?

With rain a fact of life in the UK, water resistance is essential. Strong grey mailing bags use a continuous film with sealed edges and a wide flap so water runs off rather than soaking in. They will not keep an item dry if left submerged in a puddle, but they will protect against normal showers, damp delivery vans and wet letterboxes.

Water damage is a big reason for refunds and unhappy customers. A few drops of water on a paperback might be fine; a soaked hoodie is not. A decent grey mailing bag is your first line of defence against this kind of avoidable loss.

Grey Mailing Bag Thickness vs Weight: What to Use for What?

Choosing the right thickness for your product type keeps parcels safe without wasting material. As a simple guide:

• Light T-shirts and tops: 55–60mu grey mailing bags.
• Premium shirts and knitwear: 60–65mu to avoid abrasion and corner wear.
• Jeans, joggers, hoodies: 65–70mu for better tear and puncture resistance.
• Small boxes inside bags (e.g. shoe boxes): strong 65–70mu with extra tape.
• Bedding, throws and towels: 65–70mu in larger bag sizes.

When in doubt, choose the stronger option for heavier fabrics and boxed goods. The tiny extra cost per bag is usually much lower than the cost of one damaged order.

Why Strong Mailing Bags Reduce Returns in 2026

Online returns are a growing issue. UK and global studies show that online return rates often sit around 20–30%, with clothing and fashion at the top of the list for sent-back items. A fair share of these returns are due to fit or style, but a worrying number are caused by damage, poor packaging or parcels arriving in poor condition.

Stronger grey mailing bags reduce avoidable returns by:

• preventing split parcels and missing items
• stopping water damage to clothing and textiles
• keeping garments looking neat and uncrushed on arrival
• reducing scuff marks on boxed items shipped inside bags

Every prevented damage return protects your margin and your reviews. As more big retailers now charge for returns, customers are paying closer attention to how parcels arrive. A solid, well-packed grey mailing bag sends the right message about your brand.

Can You Use a Mailing Bag for Fragile or High-Value Goods?

By themselves, mailing bags are not designed for fragile or high-value goods. They do not stop glass from cracking or electronics from denting. For breakable items, always use a suitable carton from our Cardboard Boxes range, then place the box inside a grey mailing bag if you want extra water protection and privacy.

A good rule is: if you would not be happy dropping the item from waist height inside only a mailing bag, it needs a box as well.

How Different Couriers Treat Mailing Bags (Royal Mail, Evri, DPD, Amazon)

Each courier handles parcels in a slightly different way, but they all place stress on bag strength:

• Royal Mail: small parcels may travel in mail bags, cages and sacks. Strong seals and tear resistance help bags survive this repeated handling. Their size and weight guide confirms the standard limits for small parcels, so choosing the right bag size as well as strength is important.
• Evri: a lot of sorting is automated, which means parcels move quickly along conveyors. Thin bags can tear when dragged or caught on equipment.
• DPD: parcels are often stacked tightly in vans and depots. Stronger bags cope better with compression and rubbing against other parcels.
• Amazon Logistics: high-speed operations and frequent hand-offs mean bags must cope with many touchpoints between the warehouse and the customer.

In all cases, a decent 60–70mu grey mailing bag gives you a stable base. For higher-risk loads, reinforcing the seal with packaging tape is wise.

The Most Common Causes of Mailing Bag Damage

From talking to UK retailers and watching parcels move through real networks, the main causes of bag damage are:

• using bags that are too thin for the item weight
• packing sharp or pointed products directly against the film
• overpacking one bag instead of splitting into two
• sealing bags with trapped air that bursts when compressed
• using poor-quality adhesive that lifts in transit

Most of these problems can be removed by choosing the right strength and packing carefully. It is much easier to prevent damage than to deal with returns and complaints later.

How to Pack Items Properly for Maximum Strength

Even the best bag benefits from sensible packing. Simple steps include:

• Fold neatly: fold clothing flat and tight to avoid hard corners or bulges.
• Protect edges: place boxed items centrally inside the bag, not right against the film.
• Remove air: press down gently on the bag before sealing to push out excess air.
• Seal firmly: run a hand along the flap to ensure full adhesive contact.
• Add tape for weight: reinforce with tape for jeans, footwear and boxed goods.

Strength by Size: Which Grey Mailing Bag Sizes Are Strongest?

Strength is not only about film thickness; size plays a role too. Bags that are too small for their contents are far more likely to split, even if the film is thick. For most clothing sellers, the most balanced sizes for strength and practicality are:

• 10×14 inch: single tees, light jumpers, children’s clothing.
• 12×16 inch: adult hoodies, jeans, sweatshirts, mid-weight bundles.
• 13×19 inch: hoodie and jogger sets, bulkier knitwear, multi-item orders.

These are the “workhorse” sizes that most UK fashion brands rely on daily. Having a good supply of each in a strong micron film will cover the majority of your orders.

Are Large Mailing Bags Weaker?

Large bags, such as 20×26 inch and 24×36 inch grey mailing bags, can feel floppier in the hand due to their size. That does not mean they are weaker. When made at 65–70mu, these bags comfortably handle bulky textiles, duvets, throws and wholesale orders.

The key is to avoid under-filling large bags. If there is a lot of empty space, items can slide around and create extra stress at the corners. Either size down or add extra padding to keep the contents stable.

Strength vs Opacity: Why Grey Bags Stay Fully Opaque

Opacity is a trust and privacy factor as well as a strength issue. Good grey mailing bags stay opaque even when stretched and filled, so no one can see the contents in transit. Poor-quality bags can look thin or blotchy, especially when items press against the film, which can concern customers receiving higher-value clothing or gifts.

Grey Mailing Bag Strength Compared to Boxes

Mailing bags and cardboard boxes each have their place. In simple terms:

• Use grey mailing bags for flexible, non-fragile items like clothing, textiles and soft toys.
• Use cardboard boxes for rigid, delicate and high-value items such as electronics, glassware, candles and ceramics.

Many brands now use a hybrid approach: a strong cardboard box inside a grey mailing bag. This keeps the inner box clean and dry while the grey bag takes the scuffs and dirt from the courier network.

Environmental Strength: Durability vs Material Use

There is a clear link between packaging strength and environmental impact. A bag that splits, leading to a damaged product and a return, has a far higher footprint than a slightly thicker bag that does the job properly the first time. Stronger bags:

• reduce the number of replacement items you need to ship
• cut wasted journeys for returns and re-delivery
• reduce the risk of items being discarded due to damage

At the same time, using the right size is vital. A well-fitted strong bag uses less material than an oversized one. For low-risk items like leaflets, simple textiles or packed goods going into retail stores, you may be able to switch from poly mailing bags to paper bags or party bags, keeping plastic for the jobs where it genuinely adds value.

Choosing the Right Strength for Your Shop (Buyer’s Guide)

To choose the correct strength for your business, work through these steps:

1. List your main product types: tees, hoodies, jeans, kids’ sets, bedding, boxes and so on.
2. Group them by weight and risk: light, medium, heavy; fragile, non-fragile.
3. Match each group to a micron band: light items at 55–60mu, heavier at 60–70mu.
4. Pick 3–5 core sizes: for most clothing brands, 10×14, 12×16 and 13×19 inch cover most orders.
5. Test-pack a sample: check how the bags behave through a full cycle – pick, pack, label, store, dispatch.
6. Record your decisions: create a simple chart for staff showing which bag to use for which SKU.

This approach gives you a clean, repeatable system. New staff can learn it quickly, and your packaging becomes part of a controlled process instead of guesswork at the packing bench.

Common Mistakes With Mailing Bag Strength (Avoid These)

There are a few mistakes we see again and again:

• Choosing by price only: picking the thinnest, cheapest bags without checking micron or real performance.
• Ignoring seals: focusing only on film thickness and forgetting that poor adhesive can ruin a strong bag.
• Using one size for everything: forcing coats into bags meant for tees, or small items into huge bags.
• Skipping tape: not reinforcing heavy or boxed parcels with a quick strip of tape.
• Not reviewing courier damage: failing to track how many parcels arrive damaged and why.

Avoiding these mistakes takes a little attention up front, but it saves a lot of trouble later on.

Internal Packaging Combinations for Maximum Strength

The strongest setups usually combine products from several packaging ranges. For example:

Some retailers also use a branded inner bag for presentation. Our pink mailing bags, purple mailing bags, green mailing bags and blue mailing bags are often used as an inner layer for gifting or boutique orders, while a grey outer mailing bag provides stronger protection during delivery.

• a sturdy box from our Cardboard Boxes collection, inside a grey mailing bag
• a strong grey bag sealed and then reinforced with packaging tape
• a coloured mailing bag (for branding) inside a grey mailing bag (for privacy and toughness)
• a retail-style gift bag or party bag inside a grey bag for a premium unboxing experience

Think of the grey mailing bag as the outer shell that takes the knocks so the inner packaging can focus on presentation.

Final Summary: How to Pick the Right Strength in 2026

Grey mailing bags remain one of the most efficient ways to ship clothing and soft goods in the UK. In 2026, strength is no longer just about “will it hold the item?” – it is about surviving automated networks, protecting against returns and giving customers confidence in your brand.

For most online sellers, the safest path is to choose 60–70mu grey mailing bags in a tight set of core sizes, reinforce heavier parcels with tape and use boxes for anything fragile or high value. By matching strength to product and courier, you cut avoidable damage, reduce returns and keep your packaging spend working for you instead of against you.

You can explore our full range here: Grey Mailing Bags and our wider Mailing Bags Collection, along with cardboard boxes, tape and paper bags to build the right setup for your business.

Useful Downloads

These helpful downloads give you quick, ready-to-use tools for choosing the right mailing bag sizes and planning bulk orders.

• Mr Bags – Mailing Bags Size Guide (PDF)
• Mr Bags – Bulk Order Form (PDF)
• Royal Mail Size and Weight Guide

Our Service Guarantee

• 5★ rated on Trustpilot
• Fast UK delivery
• Same-day dispatch cut-off on eligible orders
• Bulk and trade support for growing brands and warehouses
• Friendly email and message support from our UK-based team