When sourcing waterproof jackets, the most critical metric is the Waterproof Rating (measured in mm). For professional outdoor use, look for a minimum of 10,000mm to 20,000mm. Equally important is Breathability (measured in g/m²/24hrs); a rating of 10,000g or higher ensures comfort during physical activity. Additionally, verify the construction type, such as 3-layer (3L) laminates for extreme durability or 2.5-layer for lightweight portability. Ensure all seams are fully taped and zippers are YKK AquaGuard® or heat-sealed to prevent water ingress.