Somehow a wall filled with these hard ceramic balls is bulletproof. It stops bullets from penetrating through the wall and even prevents bullets from ricocheting off the wall too. It's basically the best shield against a gun we have.
Sure, sandbags can also stop bullets but Saab's Soft Armour system anti bullet wall looks like a normal wall that can be put onto any building. The technology is explained here:
Saab's Soft Armour system offers protection against ballistic penetration up to NATO 7.62 mm AP ammunition (STANAG level III). The system is a box concept filled with hard ceramic balls. The system is especially designed to enhance survivability and can be fitted to any structure prior to missions, or even retrofitted to existing structures in operational theatre.
A unique ceramic material protects against ballistic penetration. Soft Armour is a patented ballistic protection technology that provides security for people in vulnerable environments. Soft Armour also protects critical equipment and facilities. Soft Armour protects against all small arms ammunition including armour piercing. The system has a lower total cost than ceramic and composite protection, with reusability, multi-hit capabilities and high flexibility.