In Brave, it is nothing short of miraculous how Queen Elinor manages to tuck all of Merida's profusely curly, waist-length hair under a small wimple that doesn't even bulge — and of course, when Merida reveals herself at the archery tournament, her hair flows as freely as if it had never been subjected to the accursed wimple.
Finn of Adventure Time has a hat that holds a mane of blond hair bigger than himself. Later appearances have them shorter though. As well as with his Gender Flip counterpart Fionna.
•In Disney/Pixar's Up, young Ellie takes off her flying helmet to reveal a bushy head of hair, made to look bigger by "helmet hair" and static electricity.
In The Princess and the Frog, Facilier's hair is about the same height as the hat he's trying to keep it under. Hat hair is almost certainly in effect.
Rapunzel in Tangled uses this as character development - when she enters the kingdom for the first time, the long hair she had to keep for Mother Gothel's sake is immediately an encumbrance to her joining in the festivities and Flynn recruits a group of young girls to braid it until it's compact enough to be off the ground. When Gothel tricks her into returning to the tower, the unbraiding of her hair is a subtle symbol of her return to Gothel's dominance over her.