The 15A601 Fox 40 Sharx Whistle is specifically designed for outdoor use with its exceptional, clear sound and ability to be heard in all playable, weather conditions. This whistle is built from a durable, poly-carbonate and co-molded elastomer for user comfort and slip resistance. The Fox 40 Sharx Whistle was created for the extremes, making it the most preferred and trusted whistle among outdoor referees.