Wide Range of Sizes from Very Small to Extra Large

Opaque Grey Mailing Bags with Permanent Self Adhesive Strip

• Strong and Durable
• 100% Recyclable
• Made from Recycled Plastics *
• Custom Sizes, Colours, Printing with your Design and Logo available subject to Minimum Quantities

LEASE NOTE PRODUCTS ARE LISTED ABOVE IN INCHES - Need help converting to centimetres? Please use this helpful table below.

Sizing Guide - Grey Mailing Bags Sizes and Order Codes

How to Measure Mailing Bags

Measuring to find out which poly mailing bag to order to fit your item(s) is easier than first meets the eye.

Simply measure the diameter of the width of the product (or products put together), by placing a tape measure under the item being packaged, and bringing the measure to top around the centre from side to side, draw the measure together and make a note of this measurement.

Then do the same for the length of the product.

Take the width measurement and divide by 2, this will provide the width measurement of the mailing bag. Then take the length measurement and do the same, to calculate the length measurement of the mailer bag.

We then match both these measurements to the nearest mailer bag measurements available, only using sizes larger to allow for movement room, otherwise it will be difficult to insert your item.

For example, a product measuring 50cm around the circumference in the middle of the shortest side, and measuring 80cm around the circumference in the middle of longest side, will fit a 25cm x 40cm mailing bag (or 10x16inch), which we then recommend that the measurements are rounded up to the nearest size available on both dimensions to ensure some movement room, so in this case, would be the 300x400cm grey mailer bag (12x16inch Mailer Bag).

Measuring the mailing bags itself to find out what size to re-order is very simple.

Measure the width from side to side (that will be the width of the mailing bag) and then measure the length from top to bottom, but not including the additional flap piece for sealing the mailing bag, as this is only included on one side, and not included in the sizes stated on our website, and referred to as the lip measurement, usually around 5cm (2inches).

Convert cm to inches

Take the cm measurement and divide by 2.5. This gives the approximate amount in inches.

For example, 75cm divided by 2.5 equals 30 inches.

Convert inches to cm

Take the inch measurement (use 0.5 for half an inch if necessary) and multiply by 2.5. This gives an approximate measurement in centimetres.

For example 30.5 inches multiplied by 2.5 equals 76.25 (76 centimetres rounded down).

What size mailing bags for clothes?

Here are some typical mailing bag sizes that suit certain clothing; a folded shirt would fit in 13x19inch mailer, a coat would fit in 24x36inch mailer, two shoe boxes would fit in our 23x28inch mailer, for an exact match, please use our handy measuring guide, How to Measure for Mailing Bags, to check the exact size of the grey poly mailer that is needed for single items of clothing, or even a bundle of clothes.

What size mailing bag for shoe box?

A standard shoe box is around 3x7x11inches and this would usually fit in a 13x19 Mailer Bag.

Two shoe boxes would usually fit in a 21x24inch Mailer Bag or 23x28inch Mailer Bag

How to check this?

Please use our handy measuring guide, How to Measure for Mailing Bags, to check the exact mailing bag size for the shoe box that is needed.

What size mailing bags for t shirts?

One single folded T-shirt would usually be folded to fit within a 12x16inch clear shirt bag for high presentation packing, therefore the size of this clear bag could be used as a guide for which grey mailing bags could be used to mail the item.

For easy to insertion and quick packing we would recommend the following:

Garments inserted in a 9x12 clear garment bags - 10x14 Mailing Bags

Garments inserted in a 10x12 clear garment bags – 12x16 Mailing Bags

Garments inserted in 12x15 or 12x16 clear garment bags - 13x19 Mailing Bags

Garments inserted in 14x17 Clear Garment Bags – 16x21 Mailing Bags

Folded Garment inserted in 15x20 Clear Garment Bag - 18x22 Mailing Bags

Single Folded Garment inserted in 18x22 Clear Garment Bag – 21x24 Mailing Bags

This then provides plenty of space for promotional materials or returns paperwork.

If clear garment bag is not being used to present the t-shirt, the fold and package the t-shirt as you would like to present and then please use our handy measuring guide, How to Measure for Mailing Bags, to check the exact size of the mailing bags needed.

What is a poly mailing bag?

Poly Mailing Bags can either be an Opaque Mailing Bags that you cannot see through, completely hiding its contents, or a Clear Mailing Bags that clearly present the contents, which is more ideal for leaflets, catalogues, and other promotional materials, so persons can see your information without even having to open the envelope.

All mailing bags have a permanent seal strip to ensure goods cannot be tampered with during transit. Some may have a printed suffocation warning notice to ensure that bag is not left with babies and children, but this is not always needed and depends on how and where the mailing bag is being used.

Poly Mailing Bags are not to be confused with Garment Bags (or Shirt Bags) used for presenting garments professionally in the e-commerce market, as these have re-sealable strip for easy opening and closing and always contain a printed suffocation warning notice on the bags, which can be an issue when mailing catalogues, as it is usually preferred the mailer has a permanent sealing strip, so this cannot be opened and the contents tampered, and in some cases the printed warning notice, can obscure the printed document contained, resulting in a poorer presentation.

Are grey plastic mailing bags recyclable?

Yes, our grey mailing bags are LDPE plastic and can recycled in the commercial situation and usually be recycled through the home domestic recycling bins or recycle centre.

However local councils all have different rules about how plastics can be recycled, so please visit your local council website to check what currently applies for household and business recycling.

Can you reuse plastic mailing bags?

Yes, they can, providing the packaging is opened carefully, without tearing the plastic the seal is adhered too. Most poly mailer packaging bags have a single sealing strip with a permanent glue, so once this seal is used to send goods initially, then it will slightly damage the grey mailer by tearing the plastic when the bag is pulled open.

However, when using the grey poly mailer bag again (say to return unwanted items on a courier) if the bag is cut carefully open, then usually there is plenty of bag left to wrap around goods and this can then be resealed together with packaging tape.

On the other hand, e commerce mailing bags often have a double sealing strip giving two permanent sealing strips, one that the sender uses to seal the package, and a second for the buyer to use when returning goods.

These custom mailers are usually printed with e-commerce shop details and a ‘cut along the dotted line’ text to ensure the buyer opens the bag in the correct place and doesn’t damage the second sealing strip for returning the goods.

For e-commerce business, it is important to ensure staff packaging goods are correctly advised to use the most outer sealing strip when packaging goods for resale, as using the inner (second strip) does result in the outer strip not being able to be used.

If bespoke printed mailers or mailing bags with double sealing strips are needed, you have further questions, or are not sure which product will work best for you, then please reach out to our friendly advisors, either on the chat box online, by emailing sales@sapphirepackaging.com or telephoning 01702 205 999. We look forward to being of assistance.




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Bags / Mailing Bags / Polythene Mailers - Grey

* Most are made containing at least 30% recycled content with some being as high as 100%, check the spec on a specific item. 

Grey Polythene Mailing Bags (Opaque) — Practical Overview

Grey polythene mailing bags (often called poly mailers) are lightweight, flexible postal bags designed to protect goods in transit while keeping contents discreet. This collection focuses on opaque grey mailers with a permanent self-adhesive strip, offered in a wide range of sizes from very small to extra large. The material is described on this page as strong and durable, 100% recyclable, and made from recycled plastics (see notes on the product listing for any specific recycled-content details).

Because these mailers are thin, tough, and water resistant, they are commonly used for shipping soft goods such as clothing, textiles, and non-fragile items. They are also useful as an outer layer around boxed items to add weather protection and reduce scuffing during courier handling.

Grey Mailing Bags — Helpful Guide

1) Opaque grey peel-and-seal polythene mailers

These are the core products in this category: opaque grey mailing bags with a permanent self-adhesive strip. The opacity helps reduce visibility of the contents for privacy, while the peel-and-seal closure is designed to create a secure, tamper-evident style seal once pressed down firmly.

Products and sizes available on this page (by size code):

• Grey Mailing Bags No.00 / #00 (5 x 7) — compact mailer size suited to small, flat items and accessories.
• Grey Mailing Bags No.0 / #0 (6 x 9) — small mailer size for thin garments, small packs, and lightweight soft goods.
• Grey Mailing Bags No.1 / #1 (9 x 12) — a common “small clothing” size for folded tops and light apparel orders.
• Grey Mailing Bags No.1A / #1A (10 x 14) — extra room for thicker folds or multi-item small orders.

Note: the sizing table on this page lists products in inches and provides millimetre equivalents, along with order codes, thickness (gauge), and pack quantities. Use that table to match the exact size code and order code you need.

2) Thickness (gauge) options within the range

The table on this page shows different thicknesses (gauge) depending on size. Thickness affects puncture resistance and how well the bag holds up to rough handling. As a general rule, thicker mailers are better for heavier or sharper-edged contents, while thinner mailers can be suitable for light, soft items.

• Choose a higher gauge when shipping heavier garments (e.g., jeans, hoodies), multi-item orders, or items with corners that could stress the film.
• Choose a lower gauge for lightweight, soft items where minimal packaging weight and easy packing are priorities.

Case Study: Reducing Damage and Returns for Apparel Shipments

A small online apparel seller shipping mixed orders (single tees through to multi-item bundles) often sees two recurring issues: parcels arriving with scuffed outer packaging and occasional seam splits when bags are overfilled. A simple process change can reduce both problems:

• Standardise packing allowances: measure typical folded garment sizes and select two or three mailer sizes that comfortably fit those bundles without stretching seams.
• Match thickness to risk: use a thicker gauge for heavier bundles and a lighter gauge for single lightweight items.
• Improve sealing consistency: train packers to remove dust from the seal area, press the adhesive strip firmly end-to-end, and avoid sealing over folds.

In practice, these steps help reduce in-transit failures caused by overstuffing and inconsistent sealing, while keeping packing time predictable.

How to Choose the Correct Grey Mailing Bag

Step 1: Measure the packed item (not the product)

Always measure the item as it will be shipped: folded, bagged, or bundled. Record width, length, and thickness (depth). The thickness matters because it effectively increases the required bag width and length.

• Width: the widest part of the packed item.
• Length: the longest part of the packed item.
• Thickness: the depth of the bundle once packed.

Step 2: Allow space for easy insertion and a clean seal

Choose a bag that allows the item to slide in without forcing. Overfilling can stress side welds and can also prevent the adhesive strip from bonding properly. As a practical guideline, aim for a little clearance so the contents sit flat below the seal line.

Step 3: Select thickness (gauge) based on handling risk

Use the thickness (gauge) shown in the sizing table on this page to choose the right balance of durability and material use. Consider:

• Item weight (heavier items place more stress on seams).
• Item shape (corners and edges increase puncture risk).
• Courier handling (longer routes and multiple handoffs can increase abrasion and snagging).

Step 4: Decide whether you need an inner layer

Grey mailers are commonly used as the outer shipping layer. For presentation, organisation, or extra protection, some shippers place items in an inner bag (e.g., a clear garment bag) before inserting into the grey mailer. This can help keep items clean and reduce friction marks, especially for light-coloured textiles.

Packing Tips for Better Transit Performance

• Keep the seal area clean and flat: dust, fibres, or wrinkles can reduce adhesion.
• Press firmly along the full length: apply even pressure from one end to the other to ensure full contact.
• Avoid sealing over bulky folds: keep the contents below the seal line so the flap closes onto a flat surface.
• Don’t overfill: if the bag is stretched tight, move up a size to reduce seam stress.
• Label placement: apply labels to a smooth area to reduce peeling; avoid placing labels across seams.

Understanding Sizes on This Page (Inches and Millimetres)

This collection lists product sizes in inches and provides millimetre equivalents in the sizing guide table. When comparing to internal packing measurements, remember that the usable internal space can be slightly less than the stated external size due to seams and the flap area. If you are between sizes, it is usually safer to choose the next size up to avoid overfilling and to maintain a reliable seal.

Recycling and Material Notes

The product notes on this page state that these grey mailing bags are 100% recyclable and made from recycled plastics. For best recycling outcomes, remove paper labels where possible and keep the material clean and dry before placing it into the appropriate recycling stream for plastic film (availability varies by local authority and collection method).

Common Uses for Opaque Grey Mailing Bags

• Clothing and textiles: t-shirts, knitwear, sportswear, and multi-item apparel orders.
• Soft goods: non-fragile items that benefit from water resistance and scuff protection.
• Box overwrap: an outer layer around cartons to reduce moisture exposure and improve surface durability.
• Returns: when a spare seal strip or secondary closure method is used, mailers can support streamlined returns processes.

Frequently Asked Questions