Super-simplified answer: It’s an additive that increases the viscosity of the oil.
There is debate about whether this is better than just using thicker oil, which can have the same effect but without the dilution of the other additives in the oil (friction modifiers, detergents, etc.).
What’s the “trick” to this? I always played with these. Is it actually much better? More or less viscous?
Super-simplified answer: It’s an additive that increases the viscosity of the oil.
There is debate about whether this is better than just using thicker oil, which can have the same effect but without the dilution of the other additives in the oil (friction modifiers, detergents, etc.).
Edit: a word