To make neoprene, raw rubber is mixed with a “chemical blowing agent” which, under heat and pressure, releases nitrogen gas into the rubber, creating the gas “cells” that provide insulation.
On the surface, these gas cells make us buoyant, meaning we have to wear a lot of weight to be able to dive down through the first couple of meters without generating uncomfortable levels of carbon dioxide.
But once we start to descend, Boyle’s law causes these gas cells to shrink, displacing less water and therefore exerting less buoyancy. So we get heavier and heavier, making the descent easier but the swim back up harder. For deeper freedives, the difficulty of this return swim starts to become a constraint.
Therefore, the less neoprene you wear, the more comfortable your dives will be. So warmer neoprene is a big advantage.