Selecting a protection vest requires matching the NIJ (National Institute of Justice) standards to your specific threat environment. For ballistic protection, Level IIA, II, and IIIA are common for soft armor (handgun threats), while Level III and IV require hard plates (rifle threats). Material choice is critical: Kevlar (Aramid) offers excellent heat resistance and durability, while UHMWPE (Ultra-High Molecular Weight Polyethylene) is significantly lighter and provides superior protection against high-velocity rounds. For stab-resistant vests, ensure they meet HOSDB or NIJ 0115.00 standards, categorized by 'Joule' energy strike resistance.