White Hot Spikes is the 3rd upgrade in BTD4 and the 2nd upgrade of path 1 for the Spike Factory in BTD5. In BTD4, it costs $300 on Easy, $350 on Medium, and $380 on Hard, and in BTD5, it costs $765 on Easy, $900 on Medium, $970 on Hard, and $1080 on Impoppable. It enables the spike factory to pop Lead Bloons with its road spikes. They can also pop frozen bloons, notable when a Spike Factory is placed near an Ice Monkey. The spikes turn red at their tips. The ability to pop leads only requires the first tack to break through the lead layer and thus, puts the lead-popping ability of the other tacks in the spike into waste.
This upgrade returns in BTD6, functioning identically to its previous counterparts. It costs $680 on Easy, $800 on Medium, $865 on Hard, and $960 on Impoppable.
It is recommended to get the first two upgrades of path 2 (Faster Production and Even Faster Production) before getting this upgrade, as producing spike piles at a faster rate is usually more valuable than allowing them to pop lead bloons.
Even though it's called white hot spikes, and the artwork shows spikes that are white at the top and orange at the bottom, the spikes actually appear reddish-orange in the middle with black at the bottom, although the very tips are white.
MOAB-SHREDR Spikes have the picture of white hot spikes on a MOAB even though this upgrade can be reached without buying the white hot spikes upgrade (e.g. 1/3 spike factory).
The bottom of the spikes aren't hot, because they are black and not red or white.