Why does wet hair clump together?
Elastocapillary coalescence in wet hair
Physicists explained why wet hair and paintbrushes clump into neat little bundles.
The team dipped brushes of thin flexible fibres into liquid, pulled them out, and measured the bundles they formed as the liquid clung between them.
Surface tension pulls neighbouring strands together while their bendiness resists, and the balance sets how big each clump gets. Your post-swim hair is doing elegant mechanics.
Wet hair clumps are a stand-off between stickiness and stiffness.