Let's talk about modulus for a bit......it's short for modulus of elasticity, a property of solids - like carbon, steel, aluminum, etc. Modulus of elasticity is the ratio of stress over strain. With it, you can calculate how much a solid will bend under a certain amount of load -- and, oh yeah, you have to take into account the geometry of the solid as well to know how much it will bend. Ever seen an I-beam? They're shaped that way for a reason
So, given two solid chunks of carbon fiber (I know, a solid chunk of fiber? please bear with me) that are shaped exactly the same -- one is IM6 and one is IM8 - the IM6 will bend more than the IM8 under the same load, because the IM6 has a lower "modulus" than the IM8.
How much will they bend? Again, depends on the geometry of the solid and the load.
---there's a point I want to make....I'm getting to it....
So you want to design a fishing rod - where do you start? Maybe you focus on how the thing reacts under load. Say we want fast action - ok, so we know the shape that we want the rod to take under load - bends more near the tip than at the middle - so we make the rod more slender near the tip than at the middle. How slender? Depends on the modulus of elasticity. Using IM6? Make it kinda slender. Using IM8? Can make it even more slender.
Not too slender though.....it might break when that fat bass nails the spinner bait:!:
Now wait a minute - is IM8 stronger than IM6? The modulus tells us how much those materials bend, but what about how much load it can take until it breaks?
Don't know
And that's my point (well, part of it). How do IM6 and IM8 compare regarding breaking stress? Are they the same? Are they different?
I guess we're supposed to believe that the IM8 provides more "feel", because it's stiffer and it will be more efficient at transmitting information from tip of the rod to the handle than the less stiff IM6. But overall, a rod that is made with IM6 can be made just as stiff as a rod made with IM8 - maybe the IM8 rod can be made more slender and so it's lighter -- but that's only possible if the IM8 has a higher breaking strength than IM6 -- but I don't know if that's true.
And how does all the goop that holds the carbon fiber in place factor into it? What's the modulus of that stuff? How much of the rod is carbon fiber and how much is goop?
I dunno. I wish they would include all this info in the marketing fluff that they feed us.
Does anybody know? If you do, please fill me in.
CrappieKeith wrote:.....
Modulus is the material of graphite per cubic inch. NO FLUFF. STRAIGHT FACT.
Seems like pure fluff to me.

None of these comments are directed at you CrappieKeith...I just can't stand marketing crap like this.
More info about modulus of elasticity:
http://en.wikipedia.org/wiki/Elastic_modulus
Info about carbon fiber:
http://en.wikipedia.org/wiki/Carbon_fiber