Behind Armour Evaluation

This testing uses a deformable backing material, such as modelling clay, to record deformation of the armour from a defeated bullet or projectile to assess the severity of insult. This type of testing is typically used in standards to evaluate head and torso protection (ballistic-resistant helmets, hard armour plates, and vests).
When evaluating the performance of body armour, there are two critical requirements. First, to stop the projectile from penetrating and second, to assess potential trauma through the backface signature. Backface Signature (BFS) is the greatest extent of indentation in the backing material caused by a non-perforating impact on the armour. This indentation is captured using a clay backing material. A crucial factor in backing materials used for armour testing is their hardness. Armour is more easily penetrated in testing when backed by harder materials; therefore, harder materials represent more conservative test methods. The backing material used to evaluate the backface signature is Roma Plastilina™ No.1 oil-based modelling clay established for use in 1977. Since then, it has been adopted by military and law enforcement agencies for evaluating body armour and helmets worldwide. The allowable backface signature varies according to the product and test method. The backface signature is a ranking tool based on survivability metrics and does not define the severity of injury. Controls on clay temperature, compaction and handling are required to ensure consistent results as provided by Biokinetics’ Clay Equipment.

Backface signature standards include:

  • NIJ
  • VPAM
  • ASTM


BABT addresses the bodily loading from defeated ballistic strike and associates the severity of impact with injury potential. This approach differs from clay in that the armour is supported by an anthropomorphic test device that has a representative shape and dynamic compliance, or biofidelity, allowing the armour to be supported and interact with the device in a more realistic manner. The device is also instrumented to measure the dynamic response of the interaction which can be equated to injury severity and risk. For helmets, head BABT, sometimes called Behind Helmet Blunt Trauma (BHBT), can be assessed with Biokinetics Ballistic Load Sensing Headform (BLSH) (*link) that measures the forces and distribution of the shell/liner system on the skull for assessing fracture potential.  Additionally, mandible loads from facial or maxilla protection systems can be assessed with the Mandible Load Sensing Headform (MLSH) (*link).  For the torso, Biokinetics’ Blunt Trauma Torso Rig (BTTR) (*link) assesses BABT by measuring the instantaneous deformation and speed of deformation to evaluate both low and high-rate modes of injury causation. The test devices have been referenced by NATO STANAG 2920 as a means of evaluating BABT for ballistic threats.


DoP testing is a way of ranking the protective capacity of various armour solutions by evaluating the residual energy of the projectile after penetration occurs by measuring projectile’s depth of penetration into solid rods of standard Aluminium or Polycarbonate (the backing material). Depth-of-penetration testing is achieved by attaching an armour tile to a ductile backing material and firing at the target, recording the resulting depth-of-penetration (DOP) and comparing that value to a value of penetration depth achieved without the armour tile in place. The advantage of this method is that it is relatively cheap to establish performance criteria for the armour tile in question, however, its disadvantage is that the semi-infinite backing is not representative of an armour system and therefore its value is in assessing comparative tile performance. These performance criteria are derived from the measured reduction in penetration and the mass of material required to reduce the penetration depth.