Taofledermaus obtained a donated sheet of Level I (UL) fiberglass ballistic paneling, the type of stuff used in making safe rooms and banks, then gave it a try as improvised body armor.
Bullet-resistant fiberglass panels are made by numerous suppliers in their own proprietary methods but they are all pretty much just a sandwich of multiple layers of fiberglass cloth or roving bonded together with a resin under heat and pressure to form a sheet that can be cut as needed.
While a sheet is kinda pricy on its own they are still cheaper per square foot than most soft body armors like kevlar.
But just try wearing a sheet of fiberglass under your muscle shirt.
Source Article from http://www.guns.com/2016/04/29/testing-fiberglass-paneling-as-body-armor-video/