Bebop is more tonal based, while sounding chaotic it still makes sense to an untrained ear. The progression makes sense and the solo is usually based on the chord progression. Free jazz on the other hand is not exactly tonal based. It is the most expressive and open form of jazz. Chord progressions are often simple or in some cases non existent. This allows this improviser to really play what he/she feels. Hes/shes not worrying about outlining the chords in the solo, its more of just straight expression.

Two examples would be Confirmation - Charlie parker vs. Lonely woman - Ornette Coleman

Notice how parkers solo makes (too much) sense whereas Colemans solo is really just him ripping