(Source:  Index card file.  Unto Zeor, Forever)  Gen's "B" Factor.  The slowest transfer speed at which the barrier reflex is triggered -- this is an involuntary reflex, the triggering of which is bound up with the psychology of the unconscious mind.  Donor's emotional state at the instant of transfer determines where the Barrier Threshold is for that transfer.  Can control where the threshold is by controlling his/her emotional state, up to a point.  A good Donor can move his barriers anywhere from the minimum (usually a lifetime constant) to the maximum for his Order.  "You can control what transfer speed your barriers slam, but you can't stop them from slamming."  Even Ilyana felt this as a kid.