"Reactive balls" are polyurethane with additives to increase porosity (still a plastic).
And the "resin" part of the name simply means that the plastic starts out as a viscous liquid before it hardens, while the "reactive" part refers to the fact that the liquid resin reacts with the additives (some of which are plasticizers) to foam up and create the porosity, in a manner similar to those foaming home insulation plastics.
This is so that they will act like a urethane ball on the oil, and then they will hook when off the oil because of their unique surface properties.
In other words, the word "reactive" doesn't refer to how the ball reacts to the lane conditioner.
Every ball manufacturer has their own (sometimes secret) formula for the additives.
Like the word "plastic" as applied to bowling balls, this is just the moniker that the industry and/or bowling community used.
The plasticizers aren't the additives that make the resin foam up. Some remain in the ball after manufacture. In fact, the first time you sweat the ball, a lot of the stuff you see coming out of it will be plasticizers. You could sweat a brand new, unused ball, and see this seepage.
This is all my uncorroborated opinion, but I'm pretty sure I'm right....
As usual, Joe Slowinski has some good info at Coverstock Basics
"If it ain't workin', you're either throwing the ball wrong or throwing the wrong ball."
"Follow the oil!"
"Dry lanes ain't worth a shot!"
"I love the smell of lane conditioner in the morning!"
current avatar is Gabby Hayes. Looks a lot like me!