Sorry for digging up an older thread, but I have to add my long winded $0.02
**WALL OF TEXT WARNING**
Take this for what it's worth...it could be total BS, but this is what I believe based off of my experience interacting with these balls over the years....and, from what I remember on the old Usenet (before www forums and before AZB forum) from rec.sport.billiards which I personally feel had validated what I experienced....
I remember there was a thread about it, and someone had some info from someone at Aramith finally shedding light on the topic. Aramith for a long time would just tell folks they're all the same. But that can't be, if the were the same, why are they being marked differently?
The Centennials were made by Aramith, and were identical to the Super Pros. ( in those days there was some question among players as to who made Brunswick's balls) At the time, the Super Pros had the Red Triangle cue ball. Centennials had the blue circle. These were identical. They are also identical to the object balls. Later on, the Red Triangle was changed to an Aramith logo cue ball. But it was all the same.
This is all before the measles ball.
Centennials are marked blue circle only to differentiate them for branding purposes. It's to appear different, despite not being different.
Blue Circle = Red Triangle = Aramith Logo = Measles
Now, as to the Red Circle ball (assuming a genuine one)...
The Red Circle cue ball is the same diameter, same weight. However, it was made of a different resin. It was made out of the same resin as the Aramith Carom balls. It was also "finished" a bit differently.
First, on the resin. Density is the same, so weight is the same. The resin is different because it had different properties. I don't remember the engineering terms for it, but it is every so slightly more "bouncy" ...the term isn't elasticity...but something like that.
This is why the Red Circle seems to move more or react off of object balls differently (more actively) than the blue circle or redtriangle/aramithlogo/measles ball.
Most players are oblivious to this, as they never achieve a high level or just aren't sensitive to these fine differences. I've met a lot of pretty decent players who wouldn't notice much difference between a Le Pro and Triangle tip back in the day, but there was a difference you can certainly feel. So people are different in their perceptive abilities.
Anyway, back to the cueballs. Supposedly, the resin is different on the Carom balls because they are larger and heavier than pool balls. So to achieve the kind of response and interaction between the balls they're looking for - they use a slightly different resin.
The Red Circle is also finished differently. It does not have the same thick "clear" outer layer if you can call it that. It's more white to the surface if that makes sense. The polish and surface is different too.
Notice how the measles, blue circle, red triangle all are chalk magnets in humid conditions more than the red circle. For some reason, the red circles tend to cling the chalk marks less. The other balls cling chalk the same way object balls do if you hit an object ball with your cue. Throughout the years, even on the web - many players have observed the red circle stays cleaner. Fake ones are the opposite. Those get chalk stains on them, especially the really poor fakes.
Aside from that, the main factor is how they play. The red circle just plain plays different. It isn't because of diameter or weight. A lot of people say the other balls "push through" or hit the object balls more solidly. Yes, in a sense compared to the red circle which seems to deflect off OB more. The red circle is more bouncy. Again, very, very slightly but it is noticeable. Pro lever players know there's a difference.
There are a few reasons there is mass confusion on the topic --
1. Red Circles are by far the most counterfeited ball out there. So results can vary greatly. $15 for an Aramith, or $3 for a Chinese knock-off? Lotta rooms get whatever saves them money. Most players are bangers anyway and these balls are destined to hit the floor a lot and get chipped.
2. Red Circles are the most popular pool hall ball by far - thus, these balls in most pool rooms are severely worn down. Which means they are actually smaller than the other balls, and actually lighter as a result of wear through abrasion. So they draw easier, and follow worse.
You can test this by putting them side by side with other balls against a rail. OR try racking the cueball in the middle in place of the 9, 10 or 8 ball. It will have lot of wiggle room around in there.
3. There's the insidious "speed" cue balls that I've heard some call them. Or draw cue balls. These balls have a red circle on them, but they are intentionally lighter while being the same size. Some of these are just a touch too white. They aren't that sorta off-white creme that normal balls are. They are a shade whiter. It isn't as white as the vinyl fake balls you might see with a toy set. Not ultra white. Just a touch brighter than Aramiths.
Why do these exist? These balls exist because some room owners like to use them as they make the game "easier" and more fun for novice players.
It's the same reason big sloppy sewer pockets exist. They eat balls. Balls going in holes makes casual players feel better. It's more fun to make balls than to constantly miss. Frustration is not fun. Success is fun. Fun people drink more and spend more and come back more. Table manufacturers do not save a single cent making a 5" pocket instead of a 4.5"...
Your casual player who doesn't even own their own cue doesn't have fun trying to make balls on a pro-cut Diamond. 5.25" sewers with shallow angle rails gobble up balls and people feel like super stars and impress their lady friends while slamming beers. They can do all their tom cruise antics too while playing werewolves of london on the juke.
Among newbies, awesome draw = pool excellence. Drawing a ball 2 feet without a miscue is fist pump business right there.
It's the same in the bowling world. There's different pins, of different weights and materials. Bowling alleys use lighter pins of a material that react explosively relative to how they are hit compared to pins used in Professional matches. This way, a total newbie who slow rolls a ball gets action on the pins like an intermediate player might. This leads to artificially higher scores.
