How to Choose the Right Size and Material for Do Not Bend Envelopes
Match your envelope size and board weight to your contents for maximum protection at minimum cost.
Standard sizes
Quick answer
C4 with 400-600gsm board backing is the right choice for most A4 documents and prints. Choose C5 for smaller items to save on postage. Choose C3 for A3 prints (ships as parcel). Board weight of 400gsm suits documents; 600gsm+ is needed for prints and artwork. Always check total thickness stays under 25mm for Royal Mail large letter rates.
Material options
Standard for legal, corporate, and official correspondence.
Popular with creative businesses and eco-conscious brands.
Dense board insert for the highest bend resistance.
70-100% recycled content at comparable performance.
Board weight guide
GSM selection0 / 3 checked
More detail: GSM guide or hardboard vs kraft.
Postage considerations
C4 and C5 envelopes can qualify for Royal Mail large letter if total thickness stays under 25mm and weight under 750g. Heavier board weights add to total weight, potentially pushing you into a more expensive weight band. Balance protection needs against postage costs.
Every size and material
Board-backed envelopes in C5, C4, and C3 with various board weights from ProcuraPack.
Browse do not bend envelopesFrequently asked questions
C4 (324 x 229mm) fits A4 flat with clearance for the board backing.
400gsm for documents, 600gsm for prints, 700gsm+ for fine art.
Yes, if total thickness is under 25mm and weight under 750g.
White for corporate/legal. Kraft for creative/eco brands.
Yes, heavier board adds weight which can push you into higher postage bands.
Part of our guide
Product Guide: Do Not Bend Envelopes
Expert guides on rigid mailers and board-backed envelopes for protecting documents, prints, and certificates.
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