What is special about CVT ATF?

[FordFETruck]

I changed the CVT oil in my brothers Scion Iq today with him, the first CVT I've serviced. He brought me Castrol Transmax ATF/CVT universal fluid. On the back of the jugs, I noticed all of the specs it covers including being compatible for use where Dex VI, Dex III, Mercon SP, LV V and Mercon and a bunch of other non CVT related ATF. I always thought the CVT oil was its own proprietary type of blend, but what is it really and what is really in the bottle? it did make a noticeable difference in the "shift" feel, it's definitely smoother and faster reacting and no whine when it's hot like it had with the old fluid.

 

[JavierH19]

Having a metal band make hard contact with a variable pulley means you can't have it slip but you still need it to be lubricated enough so that metal on metal friction doesn't make it eat itself. So the friction modifiers are where a lot of it is. Also you need it to resist shearing a bit better as cvt transmissions have more friction and thus higher temps and they're known to blacken oil way faster than regular transmissions. You can change the oil in a jatco every 15k and it and the filter will still come out pure black every time. And they don't care too much about having the oil be thin at low temps so the viscosity index is typically lower for it on average compared to atf's.