Why extra passport pages make the booklet bulge
A passport is a bound booklet, not a stack of loose cards. Its pages are secured along one edge inside a cover, so adding sheets increases the thickness of the whole bundle. The cover can flex, but it cannot make the added paper disappear: the spine and edges have to accommodate it.
A sheet also carries more than one page surface. Folded paper can provide several numbered surfaces, but every added sheet still contributes its full thickness to the booklet. As the bundle grows, the cover sits farther from the spine and the passport can become harder to close flat.
A small change with a practical cost
That added bulk is the tradeoff for keeping visa stamps and other travel records together in one document. A well-used passport can therefore feel less like a slim wallet and more like a compact notebook—especially when its pages are packed with stamps. The extra room is useful, but it makes the booklet itself part of the luggage.
