KEVLAR: More than just the best fibre for ballistic protection

With the "Ht", "Comfort" and "H-shell" offerings, KEVLAR is today's leading product family for soft and hard ballistic protection such as bullet and fragment resistant vests, helmets and hard armour.

However, KEVLAR offers much more than just lightweight protection for police and military forces, DuPont's para-armid fibre has all the technical properties which make KEVLAR vests well adapted to the severe environtments in which thyey are required to perform. These include extrames of heat, cold and humidity (even totally saturated) during missions which demand full mobility and absence of discomfort for extended periods with total retention of protective performance.

The optimum ballistic vest is one that is able to offer a combination of several key properties simultaneously rather than just one at a time. We will review some of these properties:

1. Weight:
The lightest bullet-resistant vest can be designed with KEVLAR

Most bullet resistant vests are designed to counter 9 mm FMJ (Full Metal Jacket) bullets from pistols or submachine guns. Weight and thickness of such vests depend entirely on the ballistic resistance of their protective pack to this type of ammunition.

Fig. 1 compares the typical weights of concealable vests made with KEVLAR "Comfort", KEVLAR "Ht", KEVLAR 29 and UHMWPE (ultra high molecular weight polyethylene) unidirectinal sheet packs, all intended to defeat a 9 mm FMJ Geco bullet at 410+/- 10m/s.
Fig. 1 shows that the lightest vest to defeat 9mm FMJ Geco bullets are made of KEVLAR "Ht" and KEVLAR "Comfort".

2. Wet performance:
The ballistic resistance of KEVLAR is pratically unaffested by moisture

Any ballistic pack made of several layers of material stitched together will retain moisture after being saturated with water. The water says between the layers and acts as a lubricant, aiding a projectile to penetrate the structure. For this reason, fabrics of KEVLAR used for ballistic vests are treated with a water-repellent according to a procedure specialy developed for ballistic fabricsof KEVLAR.
3. Trauma
Vests made with KEVLAR can meet the most stringent anti-trauma requirements

A detailed casualty reduction analysis has been conducted within the police community in the US since 1972. During the more than 20 years of the survey, the lives of more than 1700 policemen have been saved because they were wearing KEVLAR vests. There was no recorded casualty as the result of trauma or excessive backface deformation of the vests during impact.
There is general agreement amoung users that 44 mm is an acceptable upper limit for backface deformation of a vest when hit by bullet.

Solutions exist to bring backface deformation down from 44 mm to 30 mm or even 25 mm if necessary. Fig. 3 compares backfaces deformation of a light and flexible 100% KEVLAR "Ht" pack without stiching (5.4 Kg/m2 pack areal density), a 100% UHMWPE unidirectional sheet pack (5.4 Kg/m2 pack areal density), and 100% KEVLAR "Ht" pack made of KEVLAR "Ht" and KEVLAR anti-trauma pack (5.55 Kg/m2 total areal density). All three packs defeated the 9 mm FMJ bullet at 410 +/- 10 m/s.

Fig 3 confirms that the use of KEVLAR anti-trauma combined with KEVLAR "Ht" brings down backface deformation under 25 mm. Trauma is reduced from 27 mm to 23 mm with only a 2.8% weight penalty versus a 100% KEVLAR "Ht" pack. The pack also keeps most of its flexibility.
Contrary to most of the anti-trauma materials generally used, such as fleece, non balistic fabrics, plastic films or sheet, foams or honeycomb structures, KEVLAR anti-trauma does not add thickness to the ballistic pack.
KEVLAR anti-trauma is a KEVLAR fabric coated with resin which contributes to the ballistic resistance of the vest.

4. Wearlife:
KEVLAR is a durable product wwhich is not affected by age

The durabilty of KEVLAR is due to the fibrès inherent high mechanical, thermal and chemical resistence.
The US National Institute of Justice has tested the ballistic of 10-year old KEVLAR vests. (NIJ, Technology Assessment Program, August 1986, vol.1, no.4: Old armor tests as good as new). Its conclusiions are that "...age alone does not cause the ballistic resistance of armor to deteriorate. Rather, the kind of care and maintenance the garment receives is a more important factor".
The German Police compared ballistic resistance (V50) of 10-year old KEVLAR vests to new ones and concluded that the fiveyears of wear did not affect the ballistic resistance of vests (Ballistische Haltbarkeit von Schutzwesten "Alter schützt so gut wie neu", PVT 9/89, by Dpl.-Phys. H.-R. Damm).
According to data collected since 1972 by the KEVLAR Survivors Club and the International Association of Chiefs of Police (IACP), more than 1700 officiers live were saved by KEVLAR body armour. Only KEVLAR aramid fibre has demonstrated more than 20 years of flawless field performance.
We can conclude from these statistic that KEVLAR vests can meet end-user expectations even after 10 years of wear. Nevertheless, we racommended a regular inspection of the vests for areas of excessive wear which could becoma damaged by accident.

5. Comfort:
KEVLAR ballistic vests are the most comfortable

The times are over when ballistic vests were stiff and heavy. The latest KEVLAR vests and particulary those made with KEVLAR "Comfort" are comfortable to wear over long periods. A ballistic pack made of KEVLAR is:
Light less heat and perspiration are generated during intensive wear.
Thin stays cool because of higher water vapour permeability and better evacuation of perspiration through the ballistic pack.
stays cool because of reduced thermal barrier effect.

Flexible perfect fit to the body

100% textile soft and breathable (compared with a stiff and sealed plastic sheet)


KEVLAR vests provide ballistic protection against the most severe types of ammunition and threats, while being the lightest, thinnest and most comfortable vests to wear.
In addition, KEVLAR provides key advantages such as non-flammability, heat resistance and high durability.
The KEVLAR vest is based on the latest technological advances and demonstrated its superiority to all other anti-ballistic materials.




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