Cleansing Foam

 is the third upgrade on the first path for the Monkey Engineer. It allows the Monkey Engineer to shoot a blob of foam that can remove Regen, Camo, and Lead properties of bloons. Only 3 blobs of foam can be on the track at once (unless the Monkey Engineer has a speed boost). If a certain amount of bloons go over the foam, it disappears, regardless of if they are Camo, Regen, or Lead.

Trivia

 * The Monkey Engineer doesn't aim the foam with his gun, so the globs of foam can come from the side or back of the Monkey Engineer.
 * There is a glitch in BTD5 mobile where the Monkey Intelligence Bureau allows the cleansing foam to pop any type of bloon and damage MOAB-class bloons in a manner similer to Road Spikes. This is likely due to the foam being able to pop Lead Bloons.
 * This upgrade makes the Engineer resemble a Glue Gunner with Glue Soak.