100 x Grey Mailing Bags | 9″ x 12″ (229x305mm) | Royal Mail Large Letter A4 Size

£4.99

Maximum value for high-volume sellers. This 100-pack of 9″ x 12″ (A4) Grey Mailing Bags is the ultimate inventory staple for professional resellers. Benefit from our best wholesale rates on these waterproof, burst-proof mailers designed specifically to minimize Royal Mail shipping costs.

Wholesale Pricing: Our most cost-effective single-size pack.
Consistency: Standardize your shipping process with reliable, high-quality mailers.
Professional Durability: Heavy-duty 60 Micron thickness for total protection.
Ready for Peak: Stock up to handle your busiest sales periods with ease.

Pack Size: 100 Bags Size: 9″ x 12″ (229mm x 305mm)

10 in stock (can be backordered)

This item is selling fast!

Why Thousands of UK Sellers Choose Packaging365

Royal Mail & Evri Ready: All our bags and boxes are tested against UK courier dimensions to help you avoid unexpected surcharges.
Dispatched in 24 Hours: We know your customers are waiting. Orders placed before 2 PM are processed the same day for lightning-fast UK delivery.
Eco-Conscious Packaging: We prioritise 100% recyclable materials, helping your small business stay green without the high price tag.
No-Hassle Returns: Not the right size? No problem. We offer a 30-day money-back guarantee for all unused packaging
Free shipping on all orders over £50

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Professional A4 Shipping Solutions – 9 x 12″ Grey Mailing Bags (Pack of 100)

Upgrade your shipping game with our premium 9″ x 12″ (229mm x 305mm) Grey Mailing Bags. Specifically designed to meet Royal Mail Large Letter guidelines, these bags are the gold standard for e-commerce sellers looking to combine professional presentation with maximum postage savings.

Why Choose Packaging365 Grey Mailers?

Maximum Postage Savings: These bags are perfectly sized for A4 documents, t-shirts, and thin books. By keeping your profile slim, you can ship as a ‘Large Letter’ rather than a ‘Small Parcel,’ saving you pounds on every order.
Professional & Opaque: Featuring a dark inner lining, these bags provide 100% opacity. Your customers won’t see what’s inside, ensuring total privacy and a professional “brand-new” look upon arrival.
Ultra-Strong Protection: Manufactured from high-density, co-extruded polymer, our bags are puncture-resistant and waterproof. Whether it’s rain or rough handling, your items stay bone-dry and intact.
Tamper-Proof Seal: Our “all-season” permanent self-seal adhesive strip creates a bond so strong it cannot be opened without leaving visible signs of tampering. Once it’s sealed, it stays sealed.

Perfect For:

Apparel: T-shirts, leggings, and baby clothes.
Media: Books, magazines, and A4-sized brochures.
E-Commerce: Ideal for eBay, Vinted, Depop, and Etsy sellers shipping non-fragile items.

Also available in our mixed size packs

Technical Specifications:

Size: 9 x 12 inches (225mm x 300mm approx)
Quantity: Pack of 100
Material: 100% Recyclable LDPE (60 Micron thickness)
Closure: Permanent Self-Seal Strip
Color: Professional Opaque Grey

The Packaging365 Guarantee: Join over 5,000 UK resellers who trust us for their supplies. Order before 1 PM for same-day dispatch and take advantage of our wholesale rates—even on smaller packs!

Additional information

Weight	0.9 kg
Pack Size (Bags)	100
Colour	Grey

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Mailing Bags Size Guide

Not sure which bag you need for your Vinted or eBay sales? Use our mailing bags size guide below to find the perfect fit for your items. All our bags are lightweight to help you stay within Royal Mail and Evri weight limits.

Quick Reference Chart

Bag Size (Inches)	Metric Size (mm)	Best For…	Royal Mail Format
9 x 12″	225 x 300 mm	T-Shirts, Leggings, Thin Summer Dresses, A4 Documents	Large Letter (if < 25 mm thick)
12 x 16″	300 x 400 mm	The “Workhorse”: Hoodies, Jeans, Coats, Small Shoe Boxes, Small Bundles	Small Parcel
16 x 21″	400 x 525 mm	Winter Coats, Boots, Larger Shoe Boxes, Multi-item “Bundles”	Small/Medium Parcel

🧥 Which bag for my item?

T-Shirts & Tops: Most single t-shirts fit perfectly in a 9×12″ bag. If the fabric is very thin, you can often keep this under 2.5cm thick to post as a Large Letter, saving you nearly £2.00 in postage!
Jeans & Trousers: Adult jeans are bulky. We recommend the 12×16″ bag. It allows room for the denim to be folded without putting stress on the seams.
Hoodies & Knitwear: For a standard adult hoodie, go for the 12×16″. If it’s an extra-thick “oversized” hoodie or a winter coat, move up to the 16×21″.
Vinted Bundles: If a buyer has bought 3–5 items, the 16×21″ is your best friend. It’s heavy-duty and large enough to keep everything together in one secure package.

📏 Top Packing Tips for Sellers

The “Air Squeeze”: Before sealing the bag, press down to remove excess air. This makes the parcel flatter and less likely to get caught in courier machinery.
The Fold Test: If your item is right on the edge of two sizes, go for the larger one. You can always fold the excess plastic over and tape it down, but you can’t stretch a bag that’s too small!
Check the Depth: Remember, Royal Mail “Large Letter” is about the thickness (25mm), not just the width. If your t-shirt is folded too “fat,” it will be charged as a Small Parcel.

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100 x Grey Mailing Bags | 9″ x 12″ (229x305mm) | Royal Mail Large Letter A4 Size