Heat sensitive,egg timer can be cooled on the counter,electronic programming timing.Do not immerse egg timer in cold water,soft boiled eggs are exactly as you like them.Graduated scales show when eggs are soft, medium or hard by sensing heat instead of time.Hard boiled eggs are no longer over cooked, so they have the perfectly colored yolks and a smooth texture.Environmental food grade plastic materials,can use long time and touch feel good.Simply put the egg timer with your egg in the water,we can know the condition of your egg as the timer's color changes,egg timer darkens as eggs cook.