"How do those hats work then? I mean, obviously it's some kind of Invisibility Spell, but it's rather clever to have extended the field of invisibility beyond the boundaries of the charmed object..."
Hermione Granger on Headless Hats[src]

The Invisibility Spell is a charm that renders a target object invisible. It creates a field of invisibility around the charmed object and thus differs from the Disillusionment Charm, which hides objects by causing them to blend into their surroundings. The invisibility field can be extended beyond the object itself as well, as shown by Fred and George Weasley's invention of Headless Hats, which, when worn, make the wearer's entire head invisible.[1]


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