Aluminium Spikes

Aluminium Spikes are dropped by Aluminium Bloons when they're popped. They drop 10 spikes. Aluminium Spikes pop double the amount of bloons normal road spikes. They can also pop frozen and metal (lead, aluminium, etc.) bloons, but they use up 2 spikes per frozen bloon, and 4 spikes per metal bloon. The exception to this is the Aluminium bloon itself, which needs a full pile of Aluminium Spikes to pop.

Trivia
For a Aluminium rush you'd basically only have to pop the first bloon. Every other bloon would get popped by the spikes they drop.