Flow Forged technology utilizes high pressure rollers that heat, stretch and fortifies the barrel to the specified width and density saving maximum weight and optimizing wheel strength.
Forged wheels, however, are created by using intense heat and pressure on a solid block of aluminum, which is pressed into a high-strength mold. The result is an optimized wheel design that outperforms cast wheels..
Basically the forged process is more costly and detailed to manufacture and the cost reflects that.
Comparing Flow Forged and Fully Forged weight wise, they are very similar. Depending on design the wheels weigh 1.2-1.5 lbs per inch of size on the wheel.
For more on weight comparison between forged and flow forged see this thread:
http://f80.bimmerpost.com/forums/sho....php?t=1020450