What is the difference between IM6 and IM7 blanks?
Here is a link to a good article that explains the difference too....The basic rod is made from either fiberglass or graphite. This material is woven into what looks like sheets of cloth. The finer the weave, the faster the action. The weave is measured in modulus. Fiberglass rods have a modulus of 6 to 13 million and graphite rods are from 33- to 60-million modulus (ie: IM6 has 33,000,000 and IM7 has 42,000,000).
A high modulus rod would be stiffer, faster, lighter and more sensitive, but will also be more brittle, much like the difference between Plexiglas and glass. All rod blanks are not created equal. A quality blank will be lightweight and engineered for a specific action.