Over the weekend, a new memorial sign was dedicated at the spot in Tallahatchie County, Miss., where 14-year-old Emmett Till was found dead after being murdered in 1955. His murder was a major catalyst for the Civil Rights Movement. Previous memorials had been vandalized and shot, leading to the use of a more durable material for this new memorial: polycarbonate. However, recent news articles about the memorial dedication have referred to it as being made of “bulletproof glass,” a common misconception.
Lite Brite Neon Studio of New York donated the sign and supplied the polycarbonate material, which it works with often, not glass, according to company partner Matt Dilling. According to a CNN news article, the sign cost more than $10,000 and weighs more than 500 pounds.
Polycarbonate is a particularly strong but lightweight and transparent plastic made of thermoplastic polymers. It is used frequently in architecture for bullet-resistant applications. It can be used on its own, as in the case of the new memorial sign, or in glass-clad polycarbonate.
Glass-clad polycarbonate is a common makeup for many products labeled as bullet-resistant glass. The laminated product involves a combination of layers of glass and polycarbonate, often with other materials such as polyvinyl butyral (PVB) or thermoplastic urethane. Other forms of bullet-resistant glazing combine multiple layers of glass and PVB.
These products are tested to UL752 with ratings from level one, which can withstand a 9 mm FMJ with lead core, up to level eight, which can withstand a 7.62 mm rifle lead core full metal copper jacket military ball (.308 caliber). There’s also a shotgun rating, which can withstand a 12-gauge rifled lead slug 12-gauge 00 buckshot (12 pellets).
“Bulletproof” glass, which has been mistakenly mentioned in several articles about the new memorial sign, does not exist because no product is completely impenetrable to bullets. While polycarbonate is often used in conjunction with glass to provide protection from bullets, polycarbonate itself is not glass. However, the new sign will provide a higher level of bullet resistance than previous signs, which have been shot through and stolen, in the case of future incidents.