STRBOXONG A4 Cardboard Envelopes 334 x 234 mm, C4 Rigid Stay Flat 400gsm Expandable Capacity Book Mailers, Royal Mail Large Letter with Peel & Seal and Rip & Strip Open (Pack of 30 + Stickers)

• ULTRA-STURDY CORRUGATED PROTECTION: Engineered with high-density F-Flute corrugated cardboard, these strong A4 envelopes are significantly more sturdy than single-layer card. The double-sided corrugated board ensures your contents do not bend during rigorous postal sorting.
• PEEL & SEAL + RIP & STRIP: Our STRBOXONG envelopes feature a high-tack Peel & Seal adhesive strip for a permanent, strong closure. The integrated Rip & Strip Open tab provides a premium, frustration-free unboxing experience for your customers.
• EXPANDABLE CAPACITY FOR BOOKS: Much more than a flat envelope, the built-in capacity creases allow these sturdy mailers to adapt to the thickness of books, catalogues, and A4 documents while maintaining their rigid and strong structure.
• ROYAL MAIL LARGE LETTER (PIP): Specifically designed to meet PIP (Pricing in Proportion) guidelines. These sturdy 400gsm mailers help you save on postage by fitting through the Royal Mail Large Letter slot, even when using the expandable capacity for thicker items.
• 100% RECYCLABLE & BONUS STICKERS: A complete eco-friendly shipping solution. This pack includes 30 100% recyclable kraft envelopes and 30 red 'DO NOT BEND' stickers to ensure your strong parcels are handled with care by every courier.

Elevate your shipping with the STRBOXONG 400gsm Rigid Stay Flat Mailers. Engineered specifically for the UK market, these 334 x 234 mm A4 envelopes provide a sturdy and strong solution for mailing sensitive items that do not bend. Double-Sided Corrugated Strength Unlike standard card envelopes, our mailers utilize high-density corrugated F-Flute board. This unique 400gsm construction is exceptionally sturdy, ensuring that your A4 documents, photographs, and certificates stay flat and protected throughout the postal network. Optimized for Royal Mail Large Letter (PIP) Every penny counts. Our envelopes are designed to meet Royal Mail Large Letter (PIP) guidelines. The expandable capacity allows the mailer to adapt to the thickness of your items—from single sheets to thick books—while staying within cost-effective shipping categories. Seamless Peel & Seal + Rip & Strip We’ve optimized both the packing and unboxing experience. The Peel & Seal strip provides a strong, permanent closure in seconds. When it arrives, your customer can use the Rip & Strip Open tab to access their items easily and safely, without needing a blade. 100% Recyclable & Professional First impressions matter. Our kraft brown envelopes are 100% recyclable and plastic-free, perfect for the eco-conscious business. To ensure your mail is handled with care, we include 30 red 'DO NOT BEND' stickers with every pack of 30 sturdy mailers.