High strength poly, this flash hider, also known as a flash suppressor, is a muzzle device that reduces the visible muzzle flash when an airsoft rifle is fired, primarily to protect the shooter's vision in low-light conditions and potentially to reduce the flash signature visible to others. 
Here's a more detailed explanation:
Purpose:
The primary function of a flash hider is to minimize the bright flash that occurs when a BB leaves the barrel, which can be blinding to the shooter and can also reveal their position to potential adversaries.