Cenospheres are a by-product from coal ash. These hollow light weight spheres are produced around the world. Most all of the cenospheres produced today are recovered from ash ponds or lagoons typically onsite at the coal fired power plant. SSI was one of the first companies to introduce cenospheres to the world on the internet. Since that time the cenospheres have become more widely used and demand has increased for the product. Since the demand has increased supply has been coming from overseas from other Countries. Some times new suppliers will have trouble developing quality control measures for the material. Having a quality product chemically and physically on a consistent basis is critical for the end use customer. If you're interesting about it , pls feel free to contact us . Thanks . +8613901803130