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Do air-gaps behind soft body armour affect protection?
  1. Lee Tilsley1,
  2. D J Carr1,
  3. C Lankester1 and
  4. C Malbon2
  1. 1Impact and Armour Group, Centre for Defence Engineering, Cranfield University, Defence Academy of the United Kingdom, Shrivenham, UK
  2. 2Mechanical Engineering, Material Science and Civil Engineering, Centre for Applied Science and Technology, Home Office Science, Hertfordshire, UK
  1. Correspondence to D J Carr, Impact and Armour Group, Centre for Defence Engineering, Cranfield University, Defence Academy of the United Kingdom, Shrivenham, SN6 8LA, UK; d.j.carr{at}


Introduction Body armour typically comprises a fabric garment covering the torso combined with hard armour (ceramic/composite). Some users wear only soft armour which provides protection from sharp weapons and pistol ammunition. It is usually recommended that body armour is worn against the body with no air-gaps being present between the wearer and the armour. However, air-gaps can occur in certain situations such as females around the breasts, in badly fitting armour and where manufacturers have incorporated an air-gap claiming improvements in thermophysiological burden. The effect of an air-gap on the ballistic protection and the back face signature (BFS) as a result of a non-perforating ballistic impact was determined.

Methods Armour panels representative of typical police armour (400x400 mm) were mounted on calibrated Roma Plastilina No 1 and impacted with 9 mm Luger FMJ (9×19 mm; full metal jacket; Dynamit Nobel DM11A1B2) ammunition at 365±10 m/s with a range of air-gaps (0–15 mm). Whether or not the ammunition perforated the armour was noted, the BFS was measured and the incidence of pencilling (a severe, deep and narrow BFS) was identified.

Results For 0° impacts, a critical air-gap size of 10 mm is detrimental to armour performance for the armour/ammunition combination assessed in this work. Specifically, the incidences of pencilling were more common with a 10 mm air-gap and resulted in BFS depth:volume ratios ≥1.0. For impacts at 30° the armour was susceptible to perforation irrespective of air-gap.

Conclusions This work suggested that an air-gap behind police body armour might result in an increased likelihood of injury. It is recommended that body armour is worn with no air-gap underneath.

  • penciling
  • perforation
  • bullet deformation
  • BFS
  • BABT

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  • Contributors CM suggested this study which was completed by LT for his MSc thesis in Forensic Ballistics with assistance from DJC and CL. DJC wrote this paper from LT's thesis. All other authors approved the manuscript.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data sharing statement The original data is in the MSc thesis of the author LT which can be obtained from DJC.