Spikes last much longer and can carry over one round.
~ Upgrade description in BTD6.
Long Life Spikes is the 3rd upgrade of Path 3 for the Spike Factory in BTD6. The spikes produced by the Spike Factory can pop the same amount of bloons as the base form (which is 5, or 10 with Bigger Stacks, plus one more if the One More Spike Knowledge Reward has been applied). However, the spikes look different, now appearing as blue spikes. These spikes can last much longer than the other spikes produced by the Spike Factory. They can last up to two rounds, or 140 seconds whichever is shorter.
Always purchase this upgrade on single-entry-single-exit maps near the end of the track. Then spikes won't be used up immediately, allowing spike stockpiling to slowly make the tower more and more valuable.