Natural feather balls from Yonex are made from Chinese geese, with the springs being by-products of the food industry. The five different products vary only in quality, indicated by a number; the higher the number, the smoother the ball flies and the longer it lasts. AS-40 and AS-50 are Swiss Badminton approved shuttlecocks for all tournaments and interclub championships in Switzerland. The AS-30 is approved for the 3rd to 5th league of the Interclub Championships and is recognized as a first-class training ball, even for unlicensed players. The AS-30 is the bestseller in the range of natural feather balls. AS-20 and AS-10 are also very good shuttlecocks, often used as training balls in clubs. Hobby players increasingly use feather balls with real feathers, as they provide a more enjoyable playing experience and a richer sound during strokes. Most Grand Prix tournaments, World Championships, and Olympic Games utilize Yonex shuttlecocks, which are the standard in both professional and recreational sports. Yonex feather balls are the best-selling balls in the world. AS-10 and AS-20 are available only in Speed 3, while AS-30, AS-40, and AS-50 are available in Speed 2, with AS-50 also available in Speed 1. Speed 3 is typically used in Switzerland, but Speed 2 is becoming more common. Speed 1 is best suited for areas like the Jura or Engadine. Other shuttles may fly far beyond the field. In badminton, the speed of the shuttle is defined by the rules or by the referee, if present. It is only affected by external geographic or meteorological factors such as temperature and humidity. The playing level or preferences of the players do not influence this, at least in terms of control technology. However, at lower levels, players often prefer slower shuttles for easier control, or faster shuttles for striking from baseline to baseline.