Fortified Bloons are a type of Bloon Modifier in Bloons TD 6. This property can be applied to Lead Bloons, Ceramic Bloons, MOAB-Class Bloons, and Golden Bloons. Fortified Bloons require more damage to pop than their non-Fortified counterparts: Fortified Leads take 4 damage to pop, while fortified Ceramic and MOAB-Class Bloons take twice as much damage to pop. If a Fortified Bloon degrades to a layer that cannot be Fortified, its children will not be Fortified (e.g., popping a Fortified Ceramic will spawn two non-Fortified Rainbow Bloons), and Fortified Regrow Bloons will not regenerate their Fortified properties if they regrow to their initial layers.
While not technically a Fortified Bloon, Diamondback's Rattle Tail is treated as Fortified by attacks that do more damage to Fortified Bloons.