Enhance your soil. Use this expandable brick of all-natural coconut fiber (coir) to improve your soil, making it easy for plants to stretch out their root systems. Loosens hard clay soil and adds water-retaining fibers to sandy soil. Resists compacting and remains porous for air circulation — the perfect, sterile growing medium. Made from coconut husks. Expands to nearly 2 gallons when you add 1 1/5 gallons of lukewarm water.