Tamper-Evident Postal Packaging Our M0-FLTR cardboard envelope mailer is designed as a "max large letter" size in the Lil "M-Spec" range, engineered to make the most of Royal Mail's large letter dimensions when packed flat, helping you avoid stepping up to a more expensive parcel tariff unnecessarily. Made from strong corrugated kraft cardboard, the M0-FLTR offers box-form rigidity in a slim, letterbox-friendly format. Pre-folded flaps and ghost creases mean fast, consistent packing every time, and the peel-and-seal tear-strip closure means you can seal orders without tape. Designed to accommodate Royal Mail's large letter tariff flat packed (164 x 239mm) — maximising the large letter allowance, or the small parcel tariff when expanded (175 x 114 x 50mm). (See our guide to large letter tariff savings for the full postage breakdown.) Our peel-and-seal closure uses a high-tack adhesive that bonds permanently on contact, unlike lower-security seals that can be carefully peeled back and reapplied without obvious signs of tampering. Once sealed, our mailers are tamper-evident: any attempt to open the parcel in transit leaves a clear, visible mark, giving your customers confidence that what arrives is exactly what was sent. Ideal for: documents, forms, greetings cards, small photo prints, and other flat or lightly bulky items where maximising the large letter tariff matters most. Lil Packaging is Europe's largest independent producer of ecommerce postal packaging. See more of our M-Range Cardboard Mailers. Product Specification: Size: 164 x 239mm (flat pack) / 175 x 114 x 50mm (expanded) Material: Corrugated kraft cardboard Closure: Peel & seal, tamper-evident Postal fit: Royal Mail Large Letter (flat, maximised) / Small Parcel (expanded) Certifications: FSC®, Plastic Free, Zero Carbon Why choose the M0-FLTR: 100% recyclable, FSC® certified, plastic-free Zero Carbon manufacturing (UK made) Peel-and-seal closure, no tape needed Designed to maximise the Royal Mail large letter allowance
