Abstract: A unitary spring system end cap packaging unit, for protecting a fragile article contained within a shipping carton, including a platform portion dimensioned to support at least a portion of a shock/vibration sensitive article, and a sidewall structure. The sidewall structure includes an inner wall with a distal edge joined to the platform portion, an outer wall and at least one spring system integrally joined to a proximal edge of the inner wall and an upper edge of the outer wall. The spring system spaces the inner wall from the outer wall. The spring system includes at least one flexible harmonic bellows forming a flexible ridge that has an arcuate shape along the length of the sidewall structure. The outer wall extends below the distal edge of the inner wall so that the platform portion is supported above the lower edge of the outer wall.