Trauma plate

A trauma plate, also known as a trauma pack, is a plate that is an add-on component/insert to a ballistic vest. Its primary purpose is to absorb and disrupt the kinetic energy of a bullet impact and reduce the blunt trauma transferred to the wearer of the vest. Trauma plates typically enhance the ballistic value (how "bulletproof" it is) of the part of the vest that they are positioned behind. Trauma plates are most commonly found in a pocket in front of the ballistic panel of a vest and positioned in the center of the chest. Some vests feature plate pockets in the back of the vest as well as the front. Some advanced tactical and demolition vests accommodate a multitude of trauma plates.

Shapes and sizes
Trauma plates can be found in a variety of sizes and shapes. The most common shapes are rectangle, rounded rectangle and irregular hexagon.

In concealed vests (vests worn under a shirt), the trauma plates are most commonly 5″ × 8″, with variants including 5″ × 7″, 5″ × 9″, 6″ × 8″, and 6″ × 9″. Thickness (depth) varies based on material and application but rarely exceed 1/4″.

In tactical vests, worn as outerwear, the trauma plates are most commonly 10″ × 12″ with some variation depending on the vest. Thickness varies, depending on material and application, but rarely approaches 1/2″.

In specialized/military-grade vests, a considerable portion of the vest is made up of rigid, trauma-plate like inserts. Since they are an essential part of the vest, they are NOT typically considered the same as trauma plates and are typically referred to as inserts, much like the aramid ballistic inserts found in concealed, duty, and tactical vests. SAPI vests are an example of this type of vest. In most SAPI based vests/carriers, the outer vest is made out of and lined with aramid material is made to carry multiple ballistic inserts, typically made out of ceramics. These inserts are shaped to fit the carrier and have sizes that vary depending on the size and shape of the vest.

Materials
Most trauma plates are made of a combination of materials. The following categories denote the primary material used in different plate packages.

Ceramic
A ceramic is a non-metallic, inorganic material, like glass - but much stronger and consisting of a variety of possible materials. Ceramic plates, typically composed of boron carbide or near variants, are very popular in military application. These materials offer very high ballistic value. However, they do not do very well at dispersing blunt trauma. As a result they are often backed with materials like aramid fabrics, high density plastics, and/or metals.

Metal
Most metal trauma plates are made primarily of steel or titanium. Aluminium and various alloys also exist. Metal trauma plates are typically considered the best for reducing blunt trauma, thanks to the conductive traits of the material.

There are stories of bullets sliding or bouncing off of metal trauma plates and injuring the wearer(shots deflected off the chest and hitting the head). As of this writing, stories of such claims are unverified and unlikely, as the trauma plate is typically positioned behind the aramid fabric/panels of the vest, and the likeliness of a bullet passing through the fabric, ricocheting, and passing through more aramid fabric is very unlikely. However, to address this fear, many metal plates are encased in special materials designed to trap the bullet and/or its fragments.

Fabric
Often called, Soft trauma plates, these are flexible plates that typically do little to reduce trauma. They are typically composed of layers of aramid fabrics, similar to, if not the same as the material found in the vest. They may also include thin sheets of metal or ultra high molecular weight polyethylene(UHMWPE) to add stiffness and some trauma protection.

Plastic
Multi-layered sheets/plates of ultra high molecular weight polyethylene (UHMWPE) can provide an added ballistic enhancement equal to or even greater than metal plates with less weight. With these, there is the cost of less trauma reduction and the improbable but possible risk of fracture. The layered sheets that exist in each plate, are sometimes separated by high density foam, which provides some compression to aid in dissipating the kinetic energy of an impact. Though this is more often found in cheap polycarbonate plates that provide some trauma reduction, but no ballistic value.
 * UHMWPE plates are often referred to as being ten times stronger than steel. UHMWPE can be strewn into a thread when made, and woven into a fabric that competes in strength, flexibility, and weight to modern aramid fabrics, and may pose as an alternate material in future vests.

Nanomaterials
Proposed to be the future for both trauma plates and anti-ballistic fabrics, carbon nanotube and nanocomposite materials offer a new strength to weight ratio that exceeds current materials. For further information on these materials as applied to ballistics, please visit the section on ballistic vest nanomaterials in ballistics. Though nanotechnology processes are used to enhance modern ballistic materials, no "nanomaterials" are currently available in commercial products.

Special Threat Plates
Special threat plates (STP), also known as multi-threat, special purpose, rifle, and special application plates, are plates that have a notably higher ballistic rating(NIJ standard) than the vest. There is no standard for materials or ballistics for these plates, though most meet the NIJ Standard for armor type III. Many of these plates are made of a combination of materials, like ceramic on plastic, plastic on metal, etc.

Some manufacturers use these labels more for marketing than really offering enhanced protection.