Back-Face Deformation (BFD)
Definition
The indentation left in Roma Plastilina No. 1 clay backing material behind an armour panel after a bullet impact that does not penetrate. Maximum 44 mm under NIJ 0101.06. Exceeding this limit constitutes test failure because the blunt trauma to the wearer's thorax at this deformation level exceeds the 25% serious-injury probability threshold from Wayne State University biomechanical studies.
- Abbreviation
- BFD
- Backing material
- Roma Plastilina No. 1 clay
- Governing standard
- NIJ 0101.06
- Maximum allowed depth
- 44 mm
- Injury basis
- Wayne State University biomechanical thresholds
Common questions
Why is clay used instead of a rigid material to measure BFD?+
Clay deforms permanently and retains the shape of the impact, so it acts as a witness record of how far the panel flexed inward against the body even though the bullet did not penetrate. A rigid backing would not preserve this deformation for measurement after the shot.
Does exceeding the 44 mm limit mean the armour failed to stop the bullet?+
No, the bullet did not penetrate in either case; the limit concerns blunt trauma, not penetration. A deformation beyond 44 mm indicates the impact transferred enough force to the wearer's thorax to carry an unacceptable probability of serious injury even without the round passing through.
How consistent is clay-based BFD testing across laboratories?+
Clay is temperature and handling sensitive, so NIJ 0101.06 specifies calibration drop tests to confirm the clay is within an acceptable stiffness range before each test series. Variation in clay conditioning between labs has been a recognised source of inter-laboratory disagreement in ballistic panel certification.
Related terms
- 10% Ordnance Gelatin (FBI Protocol)
- Porcine or bovine gelatin at 10 g per 100 mL water, chilled to 4°C, calibrated with a 4.5mm steel BB at 590...
- 20% Ordnance Gelatin (NATO Protocol)
- Gelatin at 20 g per 100 mL water, at 10°C. Higher concentration produces greater penetration resistance, modelling the full human body including...
- Clear Ballistics (Permagel)
- A synthetic polymer-based ballistic test medium formulated to match 10% ordnance gelatin at 4°C. Optically clear (allows high-speed video of bullet penetration),...
- IS 17051-2018
- The Bureau of Indian Standards specification for personal body armour, published 2018. Defines four protection levels tested against 9mm FMJ, 7.62x25mm Tokarev...
- NIJ Standard 0101.06
- The National Institute of Justice (US DOJ) body armour performance standard, published 2008. Defines five protection levels (IIA, II, IIIA, III, IV)...