Ventilation refers to the direction that the hair is knotted or injected (i.e.. left part, comb back, freestyle, etc.). Freestyle venting means that the hairs are in a random order and no set style. This allows you to experiment with styles. So whether injected or knotted is used freestyle is basically the same. When hair is knotted the cuticles are going in one direction going towards the scalp and the opposite direction going away from the scalp. Injected hair will be tend to lie flatter with just about any style that is not freestyle.
Regards,
John