Introduction
An airmail envelope is built light for international post: paper thin enough to keep the mailpiece inside a lower postage band, in a metric format for a folded A4 letter. The red and blue border is the part buyers picture, and it has done no sorting work for decades.
What makes an envelope airmail
Weight and format define the type, not the border.
| Trait | Airmail envelope | Standard business envelope |
|---|---|---|
| Paper weight | 60–80 gsm | 80–100 gsm |
| Common formats | DL, C5, C6 | #10, DL |
| Border | Often printed | Usually none |
| Finish | Uncoated, writable | Coated or uncoated |
| Design driver | Postage weight | Durability, print quality |
JAM Paper sells a #10 airmail envelope at 4.125 × 9.5 in with the traditional border, so the look travels outside metric markets.
Airmail envelope sizes
DL is the default, because it matches a business letter folded in thirds.
| Size | Dimensions (mm) | Dimensions (in) | Holds |
|---|---|---|---|
| DL | 110 × 220 | 4.33 × 8.66 | A4 in thirds |
| C6 | 114 × 162 | 4.49 × 6.38 | A4 in quarters, folded cards |
| C5 | 162 × 229 | 6.38 × 9.02 | A4 in half |
| C4 | 229 × 324 | 9.02 × 12.76 | A4 flat |
C4, C5, C6 & DL Envelope Sizes covers the C-series in full, and International Envelope Sizes sets the metric sizes against US formats.
C4 and C5 hold more paper, so a lighter stock saves less overall. C6 suits airmail note cards, where the border is part of the product.
Lightweight paper: 60 to 80 gsm
| Paper weight | Character | Where it fits |
|---|---|---|
| 60 gsm | Very light, translucent | Single-sheet letters, light ink |
| 70 gsm | Light, standard airmail | Most airmail stationery, C6 cards |
| 75 gsm | Light, better opacity | DL mail where contents may show |
| 80 gsm | Lightest business weight | Confidential or heavy-ink contents |
| 90 gsm and up | Standard envelope stock | Not an airmail weight |
Stock airmail products sit mid-range: Basildon Bond's C6 airmail envelopes are 70 gsm, and DL airmail with the block border is stocked at 75 gsm. A 100 gsm quote is a standard envelope with a border on it.
Lighter paper costs opacity and rigidity: contents shadow through, and heavy ink can ghost onto the reverse. The Envelope Paper Types & Weight Guide covers how gsm, opacity and finish interact.
International rates run on weight bands, and the envelope, letter, window film, seal and postage label all count toward that weight. Dropping a DL from 80 gsm to 60 gsm removes roughly a quarter of the paper weight, which matters when a mailpiece sits near a band edge.
The air mail border
| Border element | Typical practice |
|---|---|
| Colours | Red and blue |
| Pattern | Alternating diagonal stripes |
| Position | Both long edges, or one on a wallet |
| Width | A few millimetres |
| Function today | Decorative |
The border began as a sorting mark, from the years when air mail and surface mail travelled separately. Operators later replaced that job with a service marking: the UPU convention requires air items to carry a blue "Par avion" label, not a decorative border.
| Goal | Border approach |
|---|---|
| Traditional airmail look | Red and blue stripes |
| Brand recognition | Stripes in brand colours |
| Plain commercial mail | No border, less ink |
| Resale product | Border plus brand mark |
Printing the border
| Method | Suitability |
|---|---|
| Flexographic | Good for an edge stripe |
| Offset litho | Accurate repeat on long runs |
| Digital | Short runs, artwork changes |
| Screen | Rarely used for envelopes |
| Production point | Why it matters |
|---|---|
| Bleed past the trim | No white sliver at the cut |
| Margin from the dieline | Border survives folding |
| Pattern across the flap | Stripes meet when closed |
| Clearance at the seams | No broken stripe |
| Ink coverage on light stock | Prevents strike-through |
Airmail vs a standard DL envelope
| Factor | Airmail DL | Standard DL |
|---|---|---|
| Paper weight | 60–80 gsm | 80–100 gsm |
| Opacity | Lower | Higher |
| Border | Usually printed | Usually none |
| Surface | Uncoated, writable | Coated or uncoated |
| Best for | International post | Business correspondence |
A standard DL wins when print quality or opacity matters more than a few grams. An airmail DL wins near a band edge, or when the airmail look is the product.
Common mistakes
| Mistake | Consequence | Fix |
|---|---|---|
| Treating any DL as airmail | Wrong weight for a postage target | Specify 60–80 gsm in writing |
| 60 gsm under heavy ink | Print visible on the reverse | Move to 80 gsm or cut coverage |
| Border artwork without bleed | White sliver at the cut | Extend artwork past the trim |
| Border over the address zone | Slower machine reading | Keep the clear zone empty |
| Confidential contents on 60 gsm | Contents readable through the paper | Heavier or opaque stock |
Compliance points for international mail
| Check | Why |
|---|---|
| Address block clear of the border | Machines need a clean read area |
| Border inside the trim with bleed | Keeps the clear zone intact |
| Air service marking where required | "Par avion" label or pre-printed marking |
| Size within the operator's limits | DL, C5 and C6 fit letter formats |
| Weight inside the band you paid for | Envelope weight counts |
Rules differ by operator and change over time, so confirm the air service marking before a print run. Envelope Sizes lists our standard formats.
Ordering airmail envelopes in bulk
| Specification | Detail for the factory |
|---|---|
| Format and size | DL 110 × 220, C5 162 × 229, C6 114 × 162 mm |
| Paper | 70, 75 or 80 gsm, uncoated |
| Border colours | Traditional red and blue, or brand colours |
| Artwork | Bleed, dieline, flap continuity |
| Flap and seal | Gummed, peel and seal, wallet |
| Packaging | Bulk cartons rather than retail packs |
Cost comes down to the border (an extra print pass), the format and the paper weight, so name all three in your enquiry.
FAQ
What is an airmail envelope?
Lightweight paper, usually 60–80 gsm, in an international format such as DL. The border is styling, not a postal requirement.
Do I have to use airmail envelopes for international mail?
No. The mail has to fit the service in size and weight, and a blue "Par avion" label covers the air marking.
What size is an airmail envelope?
DL at 110 × 220 mm (4.33 × 8.66 in), with C6 at 114 × 162 mm for cards and C5 at 162 × 229 mm for A4 folded in half.
What paper weight should an airmail envelope be?
70 to 80 gsm covers most orders. 60 gsm saves the most weight but needs light ink and non-confidential contents.
Can the border be printed in our brand colours?
Yes. It can stay red and blue, follow your brand colours, or be dropped for plain commercial mail.
Can we order custom printed airmail envelopes in bulk?
Yes. Send the format, paper weight, border artwork with bleed, and the quantity for a quote.
Conclusion
Airmail envelopes come down to two specifications: paper light enough to protect the postage band, and an international format that fits the letter. The border is what buyers recognise, and printed with proper bleed it is also what sells the product.
Weigh the finished mailpiece before fixing the paper weight, then Request a Quote with the size, weight and border.
Sources
- UPU Convention Manual, air service marking: https://www.upu.int/UPU/media/upu/files/aboutUpu/acts/06-manualsInThreeVolumes/actInThreeVolumesConventionManual202507En.pdf
- Basildon Bond C6 airmail, 70 gsm: https://www.ryman.co.uk/basildon-bond-airmail-envelopes-c6-70gsm-gummed-pack-of-20
- DL 110 × 220 mm airmail border envelope, 75 gsm: https://www.envelopespackaging.co.uk/110x220mm-dl-white-wallet-gummed-airmail-block-border-75gsm-opaque-envelopes
- C5 162 × 229 mm listing: https://www.envelopespackaging.co.uk/162x229mm-c5-white-wallet-gummed-v-flap-90gsm-non-opaque-envelopes
- C4 229 × 324 mm listing: https://simplicite.macfarlanepackaging.com/229-x-324-window-c4-90gsm