The SIL-X is the ultimate juggling ball. It's a soft stage ball with a very special feature which is the result of an intense research work: 1/3 of its internal volume is filled with a special LIQUID SILICONE. The barycenter is low and the ball remains super stable on high throws and easy for foot catches and head rolling/balancing. The principle is similar to the Russian balls' although it's a very different ball. The LIQUID SILICONE, unlike any kind of grain, slides perfectly inside the ball so that even when the ball is thrown with a spin it doesn't wobble in the air. Moreover the Silicone is injected through a very small hole allowing Play to use an almost invisible plastic tapered pin as a plug. (Note to curious jugglers; although the plug can be extracted and is extremely hard to push into the ball, you should not force it inside otherwise you will not be able to recuperate it).This special LIQUID SILICONE is totally non-toxic (normally used in the food industry as a lubricant), and therefore totally safe. The outer shell of the ball is rotary moulded much like the Play stage balls with a deep set hole that holds the ??invisible plug?? firmly in place. This is undoubtedly the most advanced juggling ball on the market today!