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Why Some Ballistic Helmets Fail Testing: Exploring the Science Behind Impact Resistance

Why some ballistic helmets fail testing: what each helmet standard and specification measures, the requirements a helmet can miss, and what to ask for before you buy.

ArmorList Editorial·November 10, 2025·6 min read

Why Do Some Ballistic Helmets Fail Testing? The Science of Impact & Fragment Resistance

A ballistic helmet is tested against two different hazards: projectile penetration (bullets and fragments) and impact energy (force transmitted to the head). NIJ's helmet standard and ASTM's helmet specification each test both. A helmet fails when it misses a requirement of the standard or specification it is tested to. This guide explains what the main test documents measure, which requirements a helmet can miss, and how buyers can check performance. Our sources are the standards themselves and two government reports on the U.S. Army's helmet test protocol; we found no NIJ Advisory or Safety Notice on a helmet (checked 1 October 2026), which fits OJP's statement that NIJ's Compliance Testing Program does not currently evaluate helmets.

To look up a model's record, use Product Search.

What "Passing" Actually Means (By Test Family)

1) NIJ 0106.01 (NIJ's ballistic helmet standard). NIJ published it in December 1981, and NIJ's table of active standards lists it as active, with a revision underway. It:

  • classifies helmets into three types by level of performance;
  • sets requirements for ballistic penetration and ballistic impact attenuation, along with test sampling, test sequence, projections, openings and workmanship;
  • defines the terms its shots are judged by, including fair hit, angle of incidence and witness plate.

Note: 0106.01 uses its own three types. "Level IIIA" is a body armor level under NIJ 0101.06, so a "Level IIIA helmet" borrows a body armor name. NIJ does not currently list helmets, so there is no NIJ certificate to check: read the test report and the rounds behind it, not the label.

2) ASTM E3368 (helmets for U.S. public safety officers). ASTM's specification covers handgun and rifle ammunition and classifies helmets by resistance-to-penetration levels. It addresses resistance to penetration of the shell, fasteners and weak points, a shell ballistic limit (V50), impact attenuation, shell compression and retention system strength. Current edition: ASTM E3368/E3368M-25 (checked 1 October 2026).

3) The Army's Advanced Combat Helmet (ACH) protocol. The National Research Council describes ACH testing for resistance to penetration and backface deformation, measured as the depth of the dent in clay, with limits set separately for front and back shots and for side and crown shots, across helmet sizes and conditioning environments (ambient, hot, cold and seawater). The National Research Council describes the first article test as a "90/90 standard" (at least 90 percent probability of no penetration, at 90 percent confidence), and the lot acceptance sample sizes as based on a "4% acceptable quality level". The National Research Council notes that the ACH purchase description sets an acceleration limit of 150 g for a drop at 10 feet per second.

4) STANAG 2920 and AEP-2920 (NATO). A NATO agreement on testing and classifying personal armour. The Czech defence standard that implements it describes fragment testing with fragment-simulating projectiles (FSPs), with results reported as a V50: the velocity at which a projectile has a 50 percent chance of penetrating, the same definition MIL-STD-662F uses. A V50 is a figure, not a pass or fail; a contract sets the figure a helmet must reach.

5) VPAM HVN (helmets, visors and neck protection). VPAM, an association of European test laboratories, publishes the HVN as its test guideline for bullet-resistant helmets, visors and neck protection, built on its general guideline, the VPAM APR. Its test specimens are conditioned, among other steps, at +20 °C and 65 percent relative humidity and at +70 °C.

Why Helmets Fail: The Requirements a Helmet Can Miss

Each requirement above is a way to fail. In our reading of the documents:

  • Penetration at a fair hit. A shot that meets the standard's placement and velocity rules perforates the shell or, under 0106.01, reaches the witness plate. ASTM E3368 tests fasteners and weak points as well as the shell.
  • Too much force behind a stop. Without penetration, a helmet can still miss 0106.01's ballistic impact attenuation requirement or the ACH's backface deformation limit for that shot location.
  • Blunt impact over the limit. In the ACH drop test, a peak above 150 g fails.
  • Fragment performance below the contract figure. A V50 below what the contract sets.
  • Conditioning. The ACH protocol tests helmets after hot, cold and seawater conditioning, and VPAM HVN conditions specimens too; a helmet can pass at ambient and miss after conditioning.
  • Lot-to-lot variation. A design that passed first article testing can still fail lot acceptance testing, which the ACH protocol applies to production lots.

We found no NIJ, CJTTEC or government report that attributes helmet test failures to particular resin, fiber, curing or hardware defects (checked 1 October 2026), so we do not list causes.

Inside the Physics: How Helmets Manage Energy

A helmet's shell and its pads do different jobs, and the tests measure them separately: penetration and deformation for the shell, impact attenuation for the pads and suspension. GAO describes the ACH's seven pads as mostly "slow-memory" impact foam designed to act like a shock absorber.

Temperature matters to the pads. In a DTIC study of combat helmets and pad systems, peak accelerations on one headform were substantially higher in hot conditions than in cold or ambient ones.

On ArmorList, a product's record shows the standards it was tested to, which can include NIJ 0106.01, MIL-STD-662F or VPAM.

Buyer/Agency Verification Checklist

Our advice, stated as ours:

  • Confirm the standard named on the test report: NIJ 0106.01 or ASTM E3368 for helmets, VPAM HVN for helmets and visors, STANAG 2920 or MIL-STD-662F for a V50. Do not accept a body armor standard as proof for a helmet.
  • Check blunt-impact data against your requirement (for example, the ACH's 150 g at 10 feet per second) and confirm the pads and temperatures tested match what you will issue.
  • Ask for conditioning results (for example hot, cold and seawater) and the ballistic and impact data after conditioning.
  • Check the hardware: ask whether the tested helmets had the same mounting holes and fasteners as the ones you will buy.
  • Review shot maps (placement, angles, velocities, spacing) and any lot acceptance test summaries.
  • Traceability: serials, batch records and material certificates.

Bottom Line

"Passing" has several parts: no penetration at a fair hit, force behind the stop within the limit, a V50 at or above the contract figure, and the same results after conditioning. Name the standard you require, read the shot maps and conditioning data, and ask for the full test report, not marketing claims. Remember that NIJ does not currently list helmets, so the report is the record.

Sources

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