''IM6, IM7, etc. are trade names for particular graphite produced by the Hexcel Corporation. These numbers are not industry standards nor an indication of quality, especially since other companies use the designations to refer to graphite not made by Hexcel. At best, they allow you to compare the quality of the material used to build different rods by the same manufacturer: an IM7 rod would use better graphite than an IM6 rod if both are made by the same manufacturer. It's more difficult to say the same about rods from two different companies, since they could be made from material from completely different manufacturers.
Modulus refers to the stiffness of the graphite, not the amount of material used or the number of graphite fibers incorporated into the sheets. Buying a rod based solely on the modulus rating is a mistake because other factors must be considered, for example, if the fisherman does not want the stiffest rod for light line techniques or cranking. In addition, other qualities must be incorporated in the graphite itself and the rod must be designed correctly to ensure the best performance and durability of the rod. The other components that go into a quality rod can also add significantly to the cost.
As of both IM and modulus, the higher rating, the lighter and more sensitive the rod is, however such rods also become more brittle due to time and usage.
The most effective use in bass fishing are IM and Modulus rods when one is using lures like worms and jigs. When using faster lures, such as spinnerbaits, and crankbaits, the fisherman does not need to have the sensitivity needed when using the slow lures. The theoretical reason for a more sensitive rod when using a slower lure is that many of the strikes (or more gentle "pickups") will be harder to feel with a rod of a lower modulus rating.''