So, a lot of people don't agree with me on this, but I'm right, so they need to get over it. Anyway, here's the real deal on plastic from MVP.
I'll give you a breakdown of how it works in general from all of the research I've done over the years.
The molds are all the same for all the discs except Electron and Prism in most circumstances. So, the same mold with different plastics injected into them. What happens is, the plastic cools in the mold for a certain amount of time, then is removed from the mold and is cooled some more. This timing in fairly critical, as is external environmental factors like temperature and humidity, because as the plastic cools, it shrinks. If it cools too fast or slow, the height of the wing and shoulder can be affected, causing differences in stability.
So this is where most people assume the plastic blend is the cause of stability differences. Surely Neutron/Proton cool differently than Plasma, etc, they reason. Surely metal flake, blue, insert whatever anecdotal evidence they've found based on their small sample size of discs they've thrown, is more or less stable. The truth is, most plastics have very little affect on stability. Colors also are pretty well the same. A very high amount of metal flake could cause issues, but it would have to be a VERY high amount, and I don't think we ever see that.
Plasma/Neutron (And CN because it's identical to N) and Proton are all basically the exact same plastic from a stability perspective. They cool at the same rate.
Fission, Eclipse, and Electron have some tendencies, that affect how they come out of the mold, but even those are just tendencies and not a guarantee on how they will fly. For instance, MVP has publicly stated in a Lab Report, that due to the high concentration of glow particles in their plastic, it affects the cooling, and causes the wing to raise higher. But, because the glow particles are also heavier, it evens out the gyro affect, and just basically messes with stability from multiple directions.
That being said, for the plastics that have a different effect on cooling, MVP can try to compensate by changing the timing of when they take them out of the mold, ambient temp, etc.
So where does that leave us with plastic stability?
Well, the answer is, it is MUCH MUCH more dependent on environmental factors and on each individual run. There are (relatively) understable and overstable versions of the same mold in the same plastic type just because of other factors floating around out there. That is why you will get some people swearing that Plasma is less stable, while others will claim their Plasma is their most stable plastic. All in the same mold.
But perception often defeats reality. For instance. when MVP moved production in-house, they started experimenting with Cosmic plastic. Their first run of Relays came out way more stable than intended because they didn't quite understand how to control the environmental factors. They later publicly stated this, and have since adjusted the process and now, for the most part, all Relays, including CN that are released are closer to their actual numbers. But for a large number of people, you can't convince them of it. They threw those super stable CN Relays, so now CN is the "most stable" plastic. It's not though, it's just Neutron with mixed colors. There is no difference.
In short, the only way to find the stability you want in a certain mold is to look at the PLH and compare it to others. Do you want more stable? Pick the higher PLH. Do you want less stable? Pick the lower PLH. This is ALWAYS true regardless of plastic type.
The ONLY exception is Electron, which may start out more stable, but will always beat in faster to understable.