Corrosive Glue is the Glue Gunner's level 3 upgrade in Bloons Tower Defense 4 and the second upgrade on the first path in Bloons Tower Defense 5. It costs $255 on Easy, $300 on Medium, $325 on Hard, and $360 on Impoppable. It allows the Glue Gunner to shoot corrosive glue that pops one layer of a bloon every two seconds. Corrosive Glue can pop Lead Bloons and Ceramic Bloons, although it still does not slow down Ceramic Bloons except on mobile.