The specific product, 
Nuprol RZR non-biodegradable tracer green 3500 rounds 0.20g BBs
 
Product Details
Diameter: The BBs are manufactured at 5.95 mm diameter with a low tolerance of +/- 0.01 mm, which helps ensure reliable feeding and performance, even with "tightbore" inner barrels.
Material: They are constructed of a high-density polymer, designed to be durable and provide consistent shot performance.
Performance: According to NUPROL, using quality ammunition like the RZR series, which undergoes stringent quality control, is essential for consistent shot performance and can help fine-tune your performance with your replica.
Tracer Feature: The green color makes them glow when used with an Airsoft tracer unit, providing an exciting visual and an aiming edge during low-light or night gameplay.