When selecting metal whistles, the material directly impacts sound frequency and durability. Stainless steel (304 or 316 grade) is the industry standard for high-end sports and safety whistles due to its corrosion resistance and hygienic properties. For premium or gift markets, brass or copper offers a distinct aesthetic and a 'warmer' sound, though they may require electroplating (nickel or chrome) to prevent tarnishing. Always ensure the material is lead-free and non-toxic, as the product has direct oral contact.