Gummed envelopes use a water-activated glue that you dampen to seal. Self seal envelopes have two strips of latex glue that bond when you press the flap down, with no moisture needed. Peel and seal envelopes carry a pressure-sensitive adhesive under a protective backing strip that you peel away for the strongest, longest-lasting seal. All three do the same basic job, but they behave very differently once you are sealing hundreds or thousands of items, and the closure you pick has a real effect on your packing speed, your storage life and your unit cost.
If you are ordering custom printed envelopes for the first time, the closure is one of the few specifications that people tend to skip past. It deserves a moment of thought. Below we break down each type, where it wins, where it lets you down, and how to match the closure to the way your business actually posts things.
The three main envelope closures
Gummed envelopes
Gummed is the traditional closure: a dry strip of water-activated adhesive, usually starch or gum arabic based, running along the underside of the flap. Add moisture and it becomes tacky. Press it down and it sets.
The obvious drawback is that somebody has to wet it. In practice, nobody in a busy office is licking hundreds of flaps - they are using a damp sponge, a roller wetter, or an automated inserting machine that does the wetting for you. That last point is the key one. Gummed is the closure of choice for high-volume mailing because it is the type that works reliably with folding and inserting machine envelopes. If you run a franking and inserting setup, gummed is almost certainly what you want.
The second advantage is shelf life. Because the adhesive is inert until it is wetted, gummed envelopes can sit in a stockroom for years without degrading. If you buy a large branded print run to bring your unit cost down, gummed will still be sealing perfectly long after other adhesives have given up.
Self seal envelopes
Self seal envelopes have a strip of latex-based cohesive adhesive on the flap and a matching strip on the body of the envelope. Latex sticks to latex and to almost nothing else, so the flap will not glue itself to the contents, your fingers or the envelope in front of it. You simply fold the flap over and press.
This is fast. For anyone hand-packing a run of letters, invoices or statements, self seal removes the wetting step entirely and you can work through a stack quickly. It is a popular pick for DL envelopes and everyday business post.
The trade-off is shelf life. Latex cohesive gradually loses its grab, and the industry rule of thumb is that self seal adhesive performs best within roughly six to twelve months of manufacture. Store the envelopes somewhere hot, damp or in direct sunlight and that window shortens. If you order two years' worth of stock and leave it in a warm loft, do not be surprised when the last boxes seal poorly. Browse our range of custom printed self seal envelopes if this is the closure that suits your workflow.
Peel and seal envelopes
Peel and seal is the premium option. A band of pressure-sensitive adhesive sits on the flap, protected by a silicone-coated release strip. You peel the strip off, fold the flap down and press. The bond is immediate, very strong and genuinely tamper-evident: opening the envelope tears the paper rather than releasing the glue cleanly.
Because the adhesive is protected until the moment of use, peel and seal holds its strength far longer than self seal. It also gives the neatest, flattest finish, which matters when the envelope carries your branding and is the first thing a customer touches. The downsides are cost (it is the most expensive of the three) and waste (you are left with a pile of release strips, which are not typically recyclable with the envelope).
Quick comparison
- Gummed - cheapest per envelope, excellent shelf life, essential for automated inserting machines, but slow and messy to seal by hand.
- Self seal - fast for hand packing, no moisture needed, mid-price, but the adhesive has a limited shelf life of roughly six to twelve months.
- Peel and seal - strongest and most secure seal, longest adhesive life, tamper-evident and premium-looking, but the most expensive and it generates release-strip waste.
How to choose the right closure for your business
You run high-volume automated mail. Choose gummed. It is the only closure designed to be handled by folding and inserting equipment at speed, and the cost saving across tens of thousands of envelopes is significant.
You hand-pack day-to-day business post. Self seal is usually the sweet spot. Buy in quantities you will realistically use within a year, and store the boxes somewhere cool and dry.
You are posting cheques, contracts, sensitive documents or e-commerce orders. Choose peel and seal. The tamper-evident bond and the crisp finish are worth the extra pence per unit when what is inside matters, or when the envelope is part of the customer experience.
You are sending anything with bulk to it. The closure question changes shape once you move from flat documents to products. Board-backed, padded and pillow mailers each have their own sealing strips, and we compare them in our guide to cardboard, padded and pillow envelopes.
Closures, paper weight and postage: how they connect
Closure type is only one of three specifications that decide how well an envelope performs. The other two are size and paper weight.
Size determines what you pay Royal Mail. A DL or C5 envelope will usually travel as a Letter, while a C4 almost always falls into the Large Letter bracket, and Large Letter postage costs noticeably more. Royal Mail publishes the current dimensions and thickness limits in its size and weight guide, and we cover the practical implications in Letter or Large Letter? and in our full breakdown of C4, C5, C6 and DL envelope sizes.
Paper weight, measured in grams per square metre (gsm), decides how the envelope feels and how well it hides its contents. Most business envelopes sit between 90gsm and 120gsm. Around 90gsm to 100gsm is the standard for everyday post; 120gsm feels noticeably more substantial and is the usual choice for formal correspondence or premium branded mailings. Heavier stock also takes print beautifully, which is worth knowing if your envelope is carrying a full-colour design.
Get all three right - closure, size and weight - and the envelope stops being an afterthought and starts doing a job for you.
Frequently asked questions
What is the difference between self seal and peel and seal envelopes?
Self seal envelopes have two strips of latex cohesive, one on the flap and one on the envelope body, that bond to each other when pressed together. Peel and seal envelopes have a single strip of pressure-sensitive adhesive covered by a removable protective backing strip. Peel and seal produces a stronger, more tamper-evident seal and lasts longer in storage, while self seal is quicker to use and costs less.
How long do self seal envelopes last?
The latex adhesive on self seal envelopes is generally at its best for around six to twelve months from manufacture. It does not stop working overnight, but the grab weakens over time, and heat, humidity and sunlight all accelerate that. Order quantities you will use within a year and store the boxes flat, cool and dry.
Which envelope closure works with a folding and inserting machine?
Gummed envelopes. Inserting machines are built to wet and seal a water-activated gum strip as the envelope passes through, and this is the standard closure for automated mailroom equipment. Self seal and peel and seal flaps are not designed to be handled this way at machine speed.
Are peel and seal envelopes recyclable?
The paper envelope itself is recyclable. The silicone-coated release strip that you peel off is not typically recycled with it, so it should go in general waste. If minimising waste is a priority, a gummed envelope is the cleanest option because there is nothing to throw away.
Can you print on any closure type?
Yes. Gummed, self seal and peel and seal envelopes can all be custom printed in full colour within the print area shown on each product page. The closure sits on the flap, and your design is kept clear of the seal, so the sealing method you choose does not limit your design.
Which envelope closure is cheapest?
Gummed is normally the cheapest per envelope, followed by self seal, with peel and seal the most expensive. The gap narrows at higher volumes, and it is worth weighing the unit price against the labour time your team spends sealing them.
Order custom printed envelopes to your specification
Whatever closure suits your workflow, the envelope can still carry your branding. At Fast Printed Envelopes we print gummed, self seal and peel and seal envelopes across every standard UK size in full colour, with fast UK turnaround and low minimum order quantities. Browse the full custom printed business envelopes range, or get in touch and tell us how you post - we will recommend the closure, size and paper weight that fit.