Procision Perlite Coarse is cut with a ten mesh screen leaving all material to retain #4. Perlite ore is a naturally occurring volcanic glass containing a small percentage of water. When that ore is introduced to tremendous heat the glass liquefies and the trapped water expands creating a remarkable and versatile material. In an ongoing quest to improve the quality of our products, Aurora Innovations recognized the opportunity to begin producing another of their own materials. Success at a new venture is never easy, but they're really excited about the quality of their production.