Polythene Mailing Bags

What Are Polythene Mailing Bags?

Polythene mailing bags, also known as poly mailing bags or plastic mailing bags, are lightweight postal bags made from polythene film. They are the standard choice for posting non-fragile items such as clothing, textiles, soft goods and documents. The bags are waterproof, which protects the contents from rain and moisture during transit, and tear resistant, so they hold up well through the postal system and automated sorting equipment.

Unlike postal boxes, polythene mailing bags conform to the shape of the contents, which reduces wasted space and helps to keep postage costs down. They are significantly lighter than cardboard alternatives, which is a further saving on weight-based postal charges. The peel and seal closure means there is no need for tape, keeping packing times short and ensuring a clean, professional finish.

Available Sizes

We stock polythene mailing bags in 11 sizes, designed to cover everything from small items to large parcels. Here is a guide to the most popular sizes and what they are best suited for:

Small sizes (4.5 x 7” to 6.5 x 9”) are ideal for small accessories, jewellery, cosmetics, phone cases and other compact items. The 4.5 x 7-inch bag (114 x 178mm) fits within Royal Mail’s letter rate, making it one of the most economical options for lightweight items. The 6.5 x 9-inch bag (162 x 229mm) will comfortably hold DVDs, small books and similar items.

Medium sizes (9 x 12” to 12 x 16”) are the most popular range for e-commerce businesses despatching clothing, t-shirts, accessories and A4 documents. The 10 x 14-inch bag (254 x 356mm) is a widely used size for folded clothing and sits within the large letter threshold.

Large sizes (13 x 19” to 28 x 30”) are suited to larger clothing items, shoes, bedding, cushions and bulkier parcels. The 17 x 22-inch bag (432 x 559mm) is a popular choice for coats, dresses and multi-item orders. Our largest size, the 28 x 30-inch bag (711 x 762mm), will accommodate pillows, duvets and other large soft items.

All sizes are packed in 400 to 1,000 units, making them practical for both regular office use and high-volume despatch operations.

Grey Mailing Bags for E-Commerce Despatch

Grey mailing bags are one of the most popular packaging choices for e-commerce businesses selling through Amazon, eBay, Etsy or their own website. They are lighter and more compact than postal boxes, which keeps shipping costs down and reduces storage space in your packing area. The peel and seal closure makes them fast to pack, which matters when you are processing high volumes of orders.

For clothing sellers in particular, polythene mailing bags offer a practical advantage: they conform to the shape of the garment, keeping the overall package slim and helping it qualify for lower postal rates. A folded t-shirt in a 9 x 12-inch poly bag will typically qualify as a large letter, whereas the same item in a box would be classified as a small parcel at a higher rate.

We offer competitive bulk pricing across the full range, with most sizes usually in stock for fast despatch.

Recycled and Recyclable Plastic Mailing Bags

All of our polythene mailing bags are made from 100% recycled polythene. This means the plastic used to make them has been diverted from landfill and given a second life as packaging. Once used, the bags are fully recyclable and can be returned to most supermarket carrier bag collection points for recycling.

For businesses that want to avoid plastic entirely, our Kraft Mailing Bags are made from 100% recycled brown Kraft paper. They are biodegradable, compostable and recyclable in standard household paper recycling, making them the plastic free alternative for e-commerce despatch.

Choosing the Right Size

Choosing the right size polythene mailing bag helps protect your items in transit and keeps your postage costs down. As a general rule, choose a bag that gives your item a couple of centimetres of space on each side. Too tight and the bag may split under pressure; too loose and the item may shift around during transit.

For clothing, fold the garment neatly and choose a bag that holds it without excessive empty space. For documents, choose a bag that matches the paper size (the 9 x 12-inch bag works well for A4). For shoes and bulkier items, our larger sizes from 13 x 19 inches upwards provide the room you need.

If you are unsure which size is right for your products, request a free sample and test the fit before committing to a bulk order.

Why Buy Polythene Mailing Bags from Forms Plus?

Forms Plus have supported businesses with their printing and packaging requirements since 1981. We stock polythene mailing bags in all 11 sizes, with most lines available for same day despatch. Our pricing is competitive and transparent, with further discounts available on larger orders.

We also supply a full range of complementary products, including Kraft Mailing Bags, Padded Envelopes, Postal Boxes, Packing Tape and Labels, so you can keep all of your packaging supplies in one order.

Request a Free Sample or Contact Our Team if you would like help choosing the right size or quantity for your needs.