Sticky ad units consistently outperform static placements on a viewability and CPM basis. They also carry the

Sticky ad units consistently outperform static placements on a viewability and CPM basis. They also carry the highest implementation risk.

A sticky sidebar or footer unit that stays in view as users scroll generates viewability rates of 70-90% compared to 40-60% for standard static units. Programmatic buyers pay a premium for high-viewability inventory. Done right, this is a meaningful RPM lift.

Done wrong: a sticky unit that covers content, that doesn't have a visible close button on mobile, or that reloads on every scroll event creates a user experience that drives bounce rate up and return visits down. You can measure the short-term RPM lift and miss the longer-term audience erosion entirely.

Best practices: sticky footer on mobile with clear dismiss option, sticky sidebar only on desktop with enough page margin that it doesn't overlap text. Cap refresh rate to prevent the unit from re-requesting on every scroll.

Measure 30-day session frequency changes alongside RPM when testing sticky units. Both numbers matter.