What micron polythene mailing bag do I need?

Micron thickness determines the load capacity and tear resistance of a polythene mailing bag. Clear polythene mailing bags are manufactured from 38 micron low-density polythene: right for light loads, leaflets, and mailshots where contents visibility is needed, but not for heavy garments or multi-item orders. Standard grey, silver, blue, and coloured mailing bags are manufactured from 45–60 micron tear-proof polythene: the right grade for clothing, textiles, and soft goods at standard e-commerce weights. Grey mailing bags with integral carry handles use 50–55 micron for additional strength at the handle attachment point. When in doubt, 45–60 micron is the right default for garment despatch.

Why do polythene mailing bag seals fail in transit?

Seal failures on polythene mailing bags come down to four causes. Overfilling: when the bag is packed beyond its designed capacity, the adhesive strip is under constant tension and the peel-and-seal bond fails under vibration and compression in courier handling. Wrong micron for the load: 38 micron bags used for heavy garments or multi-item orders will deform at the seam under weight. Contaminated or cold seal surfaces: the peel-and-seal adhesive needs a clean, dry polythene surface to bond correctly; dust, moisture, or very cold temperatures at the packing bench reduce adhesive performance. Incorrect sizing: choosing the right bag height but too narrow an opening forces the folded item through the neck of the bag and puts the side seam under lateral tension.

Are polythene mailing bags tamper-evident?

Yes. Once the peel-and-seal strip is engaged, opening the bag without a cutting tool means tearing the polythene, which leaves visible damage. This is tamper evidence by mechanism, not by label or marking: no additional security seal is needed. The tamper-evident property is the same across grey, clear, white, and coloured polythene formats. For operations requiring stronger tamper evidence, such as pharmaceutical despatch or high-value goods, gummed water-activated tape applied over the seal of a box provides a more robust tamper-evident mechanism.

Are polythene mailing bags accepted by Royal Mail and UK couriers?

Yes. Polythene bags are the standard accepted format for soft goods across all major UK carrier networks. Apply the address label to a smooth, flat section of the bag exterior for reliable scan performance. Royal Mail's packaging requirements, including size and weight limits for Large Letter and Parcel formats, are published at royalmail.com. Check directly with your carrier when changing bag grade, size, or format to confirm acceptance criteria.

Can polythene mailing bags be recycled?

Polythene mailing bags are not recyclable in standard UK kerbside council collections. They are recyclable via specialist plastic film recycling collection points at the front of most large supermarkets. The polythene (LDPE) is recycled into new plastic film products. This is a genuine limitation compared to paper and kraft mailing bags, which go into kerbside paper and cardboard recycling with no separation needed. Operations communicating sustainability to customers should factor this end-of-life difference into the choice between polythene and paper.

What is the difference between grey and clear polythene mailing bags?

The material and structural properties are the same grade for grade. Grey bags at 45–60 micron are opaque: the contents are completely hidden, giving privacy to the shipment and a professional finish preferred by most clothing and fashion brands. Clear bags at 38 micron are transparent: the contents are visible without opening, which suits warehouse picking and mailshot despatch where the contents are part of the visual communication. The micron difference matters: clear bags are thinner and not right for the same load weights as grey bags.

When should I use polythene mailing bags rather than paper mailing bags?

Choose polythene over paper when full waterproofing is needed for moisture-sensitive contents, when cost per unit at high volume is the primary constraint, or when the recipient's recycling behaviour cannot be influenced and specialist film recycling is more accessible than kerbside paper recycling for that geography. Choose paper over polythene when kerbside recyclability at the recipient is a brand requirement, when a sustainability certification is part of the product offering, or when FSC or PEFC certified paper sourcing is needed for procurement compliance. Both formats are accepted by Royal Mail and all major UK couriers for soft goods despatch.

Polythene Mailing Bags

Your guide to protecting products with our polythene postal bags and plastic mailing bags

Plastic mailing bags, poly mailers, and polythene postal bags for courier and Royal Mail despatch of clothing, soft goods, and non-fragile e-commerce orders. Manufactured from low-density polyethylene (LDPE) in three thickness grades: 38 micron for clear lightweight bags and mailshots; 45–60 micron for standard grey, white, and coloured plastic mailing bags for garment and soft goods fulfilment; and 50–55 micron for grey mailing bags with integral carry handles. Fully waterproof, tamper-evident on opening, and the lowest cost-per-unit flexible despatch format. Several grades contain recycled LDPE , including 30% recycled content options and grades manufactured from 100% recycled plastic , and all polythene mailing bags are recyclable via specialist plastic film collection at supermarket front-of-store points. Available from 216×356mm for single items through to 711×589mm for large parcel and bulky orders. Plastic postage bags, poly mailer bags, grey mailing bags, grey postage bags, and plastic parcel bags are all polythene mailing bags in different colour and thickness configurations. Used by fashion retailers, e-commerce fulfilment centres, subscription box operations, and catalogue businesses across the UK. Next-day UK delivery.

Polythene mailing bag micron guide

Micron (µ) is the thickness measurement for polythene film. Higher micron means thicker, stronger, more tear-resistant polythene. All poly mailers, plastic mailing bags, and polythene postal bags are graded by this measurement. Choosing the wrong micron for the load is one of the primary causes of transit seal failure.

38 micron: clear polythene mailing bags

38 micron low-density polythene for light loads, leaflets, and mailshot despatch where contents need to be visible through the bag. Right for promotional mailings, lightweight flat items, and brochure despatch. Not right for garments, heavy clothing, or multi-item orders: at 38 micron, the bag will deform at the seam under garment weight, and the thinner film increases the risk of seal failure. Clear polythene mailing bags in this range start at 165×230mm and 230×305mm internal dimensions.

45–60 micron: standard plastic mailing bags for clothing and soft goods

45–60 micron tear-proof low-density polythene: the right grade for plastic mailing bags for clothes, soft goods, textiles, and standard e-commerce fulfilment. At this thickness, the polythene handles the tear resistance demands of normal courier handling, drop impact, and compression in transit sorting. This range covers grey, white, black, silver, blue, and other coloured plastic mailing bags. The most widely used plastic mailers for high-volume garment fulfilment in the UK. Colour choice within this grade is a security and branding decision, not a structural one: all colours perform identically at equivalent micron.

50–55 micron: grey mailing bags with carry handles

50–55 micron tear-proof polythene with integral carry handles for customer convenience at the point of delivery. The marginally higher micron gives additional strength at the handle attachment point, which is a stress concentration under load. Same opaque grey finish and tamper-evident peel-and-seal closure as standard grey mailing bags. Available from 216×356mm to 711×589mm.

Choosing the right colour: plastic mailing bag security and branding guide

Within the 45–60 micron grade, all plastic mailing bag colours perform identically for tear resistance, waterproofing, and seal strength. Colour is a security, privacy, and brand decision. Here is the operational rationale for each finish.

Grey plastic mailing bags

The most widely used plastic mailing bags for clothes and general e-commerce despatch in the UK. High-opacity grey polythene keeps contents completely invisible throughout transit, from packing bench to doorstep. No indication of what is inside reduces the risk of targeted theft or tampering on busy courier routes. The neutral grey finish gives a professional, brand-consistent exterior for fashion and retail operations that do not print their bags. The default choice for any operation without a specific reason to use another colour.

Black plastic mailing bags

Black mailing bags provide maximum opacity: black polythene is the most effective colour for concealing contents and eliminating any silhouette visibility that can occur with lighter grey bags when held up to bright light. The preferred choice for high-value goods, discreet despatch of sensitive items, and any operation where complete content concealment is a security requirement. Black plastic mailers also work as a premium finish for luxury retail and fashion brands where the bag exterior is part of the customer experience. The black 100% recycled plastic mailing bags are manufactured entirely from recycled LDPE, making this colour the strongest recycled-content option in the range.

Silver plastic mailing bags

Silver mailing bags use opaque silver polythene with a distinctive metallic finish, used by fashion and retail brands where the bag exterior is a brand signal rather than purely functional packaging. Same opacity and security properties as grey: contents are fully concealed. Silver plastic mailing bags are available at 45–60 micron from small garment bag sizes through to large parcel bag formats.

White plastic mailing bags

White mailing bags use opaque white polythene for a clean, printable exterior: the preferred base for custom printed plastic mailing bags where the bag surface carries branding, returns information, or address labelling printed directly onto the polythene. White bags at 45–60 micron provide the same content concealment as grey. For custom printed plastic mailing bags for clothes or e-commerce fulfilment, white is the standard base colour. Contact the RAJAPACK Specials team on 0800 630 06 21 for custom print specifications.

Clear plastic mailing bags

38 micron transparent polythene where the contents are visible through the bag. Clear plastic mailing bags are not a security format: anyone handling the bag in transit can see what is inside. They are right for three specific applications: promotional mailshots where the recipient seeing the contents before opening is the intended communication; warehouse picking where packers visually confirm the item before sealing; and retail point-of-sale packaging where the product is part of the display. Clear bags are lighter and thinner than opaque formats and are not right for the same load weights as 45–60 micron grey or black bags.

Coloured plastic mailing bags (blue, pink, and others)

Coloured plastic mailing bags in blue, pink, and other shades serve two purposes: HACCP colour-coding on multi-product packing lines, where different colours identify different product categories or despatch routes; and brand differentiation for operations where a distinctive colour is part of the customer recognition strategy. At 45–60 micron, coloured bags perform identically to grey in transit.

Sizing guide: how to choose the right polythene mailing bag size

The most common sizing mistake is choosing the right bag height but an insufficient opening width. When a folded garment is forced through a too-narrow opening, the side seam is placed under lateral tension, which causes seam tears in transit even at the right micron grade. Always check the internal opening width before ordering.

Size guide for clothing despatch: single folded t-shirt or lightweight top, 250×350mm to 300×400mm; heavier garments such as shirts, jumpers, and formal wear, 350×450mm to 400×500mm; knitwear, hoodies, and outerwear, 450×550mm and above; multi-item orders and bulk garment packs, 500×700mm to 711×589mm. Sizes are internal opening by internal height. Add a 10% margin to the folded dimensions of the item before selecting bag size. For postage bags for clothes or plastic mailing bags for clothes in a plastic-free paper format, see paper mailing bags.

When to use polythene mailing bags and when not to

Polythene mailing bags and poly mailers are the right format in three situations where paper or padded alternatives are not adequate or appropriate.

Where full waterproofing is needed: polythene is the only flexible mailing bag material that provides complete moisture protection. Paper and kraft mailing bags are moisture-resistant and handle standard transit conditions, but will not protect contents through sustained wet exposure. For moisture-sensitive contents such as electronics, documents, or goods that are damaged by any water contact, polythene is the only appropriate flexible bag material.

Where cost per unit at high volume is the primary operational constraint: polythene mailing bags at 45–60 micron are the lowest cost-per-unit flexible despatch format. At very high volumes, the cost difference versus paper becomes significant. Operations switching to paper for sustainability reasons should model the weight and cost-per-unit difference before committing to a full format switch.

Where tamper evidence by mechanism is needed without additional security features: the peel-and-seal strip is tamper-evident by the destruction of the bag on opening. No extra label, tape, or seal is needed. For higher-security requirements, water-activated gummed tape over a corrugated carton provides a stronger tamper-evident mechanism.

Where reducing virgin plastic use is a sustainability objective without switching material entirely: several grades in the RAJAPACK polythene mailing bag range contain recycled LDPE content. The recycled polythene mailers and black 100% recycled plastic mailing bags are manufactured from 100% recycled LDPE. The Polytuf opaque mailing bags and blue plastic mailing bags contain 30% recycled content. All grades retain the same waterproofing, tear resistance, and tamper-evident seal as standard LDPE. Recyclability route for all polythene grades , including recycled-content grades , is specialist plastic film collection at supermarket front-of-store points, not kerbside.

When not to use polythene mailing bags: for fragile or valuable items that need cushioning, use padded jiffy bags. For flat rigid items that must not be bent, use cardboard mailers. For operations where kerbside recyclability at the recipient is a brand requirement, use paper mailing bags. Polythene is not kerbside recyclable in standard UK council collections.

RAJAPACK polythene mailing bag credentials

RAJAPACK has supplied plastic mailing bags and poly mailers to thousands of UK businesses over more than 70 years in packaging, including fashion retailers, fulfilment centres, subscription box operations, and catalogue businesses. Independently certified to ISO 9001:2015 for quality management and ISO 14001:2015 for environmental management. Gold EcoVadis sustainability rating: top 5% of companies assessed globally. 98% next-day delivery success rate. Custom printed plastic mailing bags in grey, white, and other colours are available through the RAJAPACK Specials team on 0800 630 06 21. Full certifications at RAJAPACK certifications and trade memberships.

Polythene mailing bags FAQs

What micron should I choose for polythene mailing bags?: 38 micron for clear lightweight bags and mailshots. 45–60 micron for all standard clothing and soft goods despatch in grey, white, or coloured formats. 50–55 micron for bags with integral carry handles where the handle attachment point needs additional strength. Using a lighter micron than the load weight needs is one of the primary causes of transit seal failures. When in doubt, 45–60 micron grey is the right default for garment fulfilment.
Why is the peel-and-seal failing on my mailing bags?: Four things cause peel-and-seal failure on polythene mailing bags: overfilling (bag under tension at the seal under load); wrong micron for the weight; contaminated or cold seal surface (dust, moisture, or cold ambient temperature reduces adhesive performance); and incorrect sizing (forcing oversized contents through a too-narrow opening stresses the side seam). Check all four before concluding the bag itself is defective.
Are grey mailing bags or clear mailing bags better for clothing?: Grey polythene mailing bags at 45–60 micron are the right choice for clothing despatch. They are opaque (contents hidden, professional finish), the correct micron for garment weights, and tamper-evident. Clear polythene mailing bags at 38 micron are thinner and designed for lighter loads and mailshots where visibility of contents is useful: they are not the right grade for garment despatch. Using clear 38 micron bags for clothing is a common cause of seal and seam failures.
Can I recycle polythene mailing bags?: Not in standard kerbside collections. All polythene mailing bags , including recycled-content grades , recycle via specialist plastic film collection, available at front-of-store points at most large UK supermarkets. They are not accepted in the kerbside paper and cardboard bin. If kerbside recyclability at the recipient is a brand requirement, paper and kraft mailing bags are the appropriate format. Where reducing virgin plastic use is the objective, 30% and 100% recycled LDPE grades are available in the range , see recycled polythene mailers and black 100% recycled mailing bags. OPRL guidance on plastic film recycling is at oprl.org.uk.
Do polythene mailing bags work for post office and Royal Mail despatch?: Yes. Polythene mailing bags, poly mailers, and plastic parcel bags are accepted by Royal Mail for soft goods and non-fragile items at standard size and weight limits. Post office mailing bags and poly bags for shipping at 45–60 micron polythene are also accepted by all major UK couriers. Put the address label on a flat, smooth area of the bag for reliable scan performance. Royal Mail's current packaging guidance is at royalmail.com/packaging-guidelines. For the full mailing bags range, see all mailing bags and envelopes.
What is the difference between polythene mailing bags and paper mailing bags?: Polythene bags (LDPE) are fully waterproof, the lowest cost-per-unit format, and not kerbside recyclable. Paper and kraft bags are moisture-resistant (not waterproof), marginally higher cost, and kerbside recyclable with cardboard. Both are accepted by Royal Mail and couriers for soft goods. The choice comes down to whether waterproofing or kerbside recyclability matters more for the operation. See paper mailing bags for the full plastic-free range.

RAJAPACK stocks polythene mailing bags, poly mailers, and plastic postage bags in all micron grades and colours with next-day UK delivery. For custom printed plastic mailing bags, contact the Specials team on 0800 630 06 21. For the full range of despatch bag formats, see all mailing bags and envelopes. Content last reviewed: March 2026. Maintained by the RAJAPACK UK Packaging Advice Team.