Where does this come from, and can I check it?

Dextrin from cooked starch turns tacky when the flap is moistened. The figure is taken from Smithsonian Institution, which is linked in full on this page. Every fact on Mondo Knows names its source rather than repeating an unsourced claim.

Is this really a everyday life fact?

Yes. It sits on the Everyday Life shelf, one of 2,600 sourced facts grouped into space, animals, the human body, history, science and more. Category pages collect every fact in the same field.

What else can I read about it?

The links under the fact point to a quiz, game, puzzle or calculator on the same subject, and the shelf below shows related facts. The wording here is original, and quoted phrases are marked as quotations.

Mondo Knows Facts

Envelope gum is a starch adhesive activated by water

Dextrin from cooked starch turns tacky when the flap is moistened Traditional envelope flaps carry a thin film of dextrin, a starch derivative that flows when wetted and sets as it dries. Modern peel and seal envelopes instead use a pressure sensitive acrylic strip covered by release paper, which needs no moisture at all. The change removed the taste of gum but made the seal harder to open without tearing. It sits in Mondo's everyday life collection, one of 200 facts that each trace back to the reference below.

Where this comes from

Smithsonian Institution

Facts that can change over time are reviewed and updated. If something here looks wrong, Mondo would rather know than be confidently incorrect.

Go further

General Knowledge trivia Technology trivia

More facts like this

Post-it notes use low-tack microscopic adhesive spheresWeak microsphere adhesive permits sticky paper strips to peel cleanly without damage A postcode splits into outward and inward codesThe first group sorts to a district, the second to a few streets A letter plate hinges inward over a hoodThe flap sheds rain while the hood keeps water off the opening itself ZIP in ZIP code stands for Zone Improvement PlanThe five digit code arrived in 1963 to speed up mechanical mail sorting HB on standard pencils indicates a balanced medium lead hardnessPencil letters H and B measure graphite hardness and blackness intensity Standard ballpoint pens rely on gravity to feed ink downwardGravity draws heavy ink to the revolving ball tip of common pens

Tags: post, adhesives, stationery

Envelope gum is a starch adhesive activated by water: the short answers

Where does this come from, and can I check it?: Dextrin from cooked starch turns tacky when the flap is moistened. The figure is taken from Smithsonian Institution, which is linked in full on this page. Every fact on Mondo Knows names its source rather than repeating an unsourced claim.
Is this really a everyday life fact?: Yes. It sits on the Everyday Life shelf, one of 2,600 sourced facts grouped into space, animals, the human body, history, science and more. Category pages collect every fact in the same field.
What else can I read about it?: The links under the fact point to a quiz, game, puzzle or calculator on the same subject, and the shelf below shows related facts. The wording here is original, and quoted phrases are marked as quotations.