Recently I have had several inquiries about GRP (Glass Reinforced Polymer, or “fiberglass”) armor. It’s important to review this material, as it is becoming more prevalent in the armoring world. It has advantages in certain applications, but is totally unsuitable in others.
GRP has been around for a while. Some of the first body armor and vehicular armor utilized this material. It is comprised of woven, large-denier S-Glass fibers in a resin (usually epoxy, but often polyester or similar). The panels are rigid, and range from a few millimeters to over an inch thick.
In applications such as structural hardening and vehicular armoring, this material is very suitable, as S-Glass is much less expensive than either Aramid or UHMWPE reinforcement. It also has excellent environmental stability, able to withstand long periods of exposure to the elements without appreciable degradation or maintenance.
Recently however, this material has begun to be re-introduced as body armor, either in standalone applications as “handgun resistant” plates, or as the backing component to ceramic rifle plates. In my experience, this material is to be avoided as personal armor.
First and foremost, during a ballistic event, glass fibers are thrown off at high velocity. Unlike Aramid fibers, these can embed themselves in the wearer, requiring exploratory surgery to remove (since glass fibers do not show up on X-ray). A projectile defeat of the plate will pull additional secondary glass fiber projectiles into the wound, complicating it.
Secondly, in handling. This material often has “slivers” or “splinters” of glass fibers standing proud from the surface. These are a non-inconsequential hazard.
Finally, GRP armor is nearly twice as heavy as an equivalent Aramid panel, and three times the weight of UHMWPE for its protection.
My advice would be to spend a little extra to ensure you are getting either Aramid or UHMWPE plates, and avoid rifle plates that specify GRP backing.
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