Partial hydration only hydrates interactive components. Static content stays as HTML.
Full hydration problem: Every component hydrates, even static text and images.
Partial hydration solution: Mark components as interactive. Only those hydrate.
Islands architecture:
- Sea of static HTML
- Islands of interactivity
- Each island hydrates independently
Frameworks: Astro, Fresh, Marko use this pattern.
Interview tip: Discuss partial hydration as an optimization for content-heavy sites with limited interactivity.