All Board and Half Board Envelopes

Cardboard envelope size guide

162 x 229mm (C5): A5 items (148 x 210mm), greetings cards, art prints, photos, vouchers · all-board or board-backed
229 x 324mm (C4): unfolded A4 documents, certificates, legal papers · all-board or board-backed
248 x 330mm (A4+): A4 documents with room for a backing card, brochures, catalogues, magazines · all-board

C sizes are envelope sizes made for A-size paper: C5 holds A5 flat and C4 holds A4 flat. Choose A4+ when an A4 sheet needs a backing card or a little room around it.

All-board or board-backed?

An all-board envelope is rigid board on both sides. Our C5 and A4+ all-board envelopes are 350gsm white coated board with a peel-and-seal strip on a 45mm lip, and the recipient opens them with a tear strip. They give the most protection to prints and photos.

A board-backed envelope has a heavy-duty manilla paper front and a board back. It is lighter than an all-board envelope, so it is cheaper to post, and the manilla front takes pen and address labels. ‘Please do not bend’ is printed in red on the front.

Posting as a Large Letter

All three sizes are within the Royal Mail Large Letter length and width limits (353 x 250mm). The packed envelope must also be no thicker than 25mm and no heavier than 750g. For thicker items such as books, use a corrugated book mailer, which folds to the depth of the item. For small items that need cushioning rather than stiffness, use padded envelopes.

Who uses cardboard envelopes

Photographers, artists and print shops sending prints; schools and universities sending certificates; offices sending contracts and legal documents; and online sellers sending art prints and greetings cards.

Trade and bulk orders

Packs of 20 let you try a size; boxes of 100 or 125 suit regular senders. For repeat or larger orders, contact us.

Frequently asked questions

What size cardboard envelope do I need for A4?
C4 (229 x 324mm) holds A4 flat. A4+ (248 x 330mm) leaves room for a backing card.

What size fits A5?
C5, 162 x 229mm. A5 is 148 x 210mm.

How do they seal and open?
Both types close with a peel-and-seal strip, so no tape is needed. The all-board envelopes open with a tear strip.

Can a cardboard envelope go as a Large Letter?
Yes, if the packed envelope is no thicker than 25mm and weighs no more than 750g.

Board-backed or all-board: which is cheaper to post?
Board-backed. The paper front makes it lighter than an all-board envelope.