Material: Clay pebbles, also known as hydroton or expanded clay pellets, are small, lightweight, and porous spheres made from heated clay. This particular medium-grade version consists of medium particles ranging from 4mm-8mm in size, making it more versatile for specific uses than larger grades.Texture and Structure: These fine-grade pebbles are lightweight yet sturdy, with a rough, porous surface. Their porous structure allows for excellent aeration and water retention, which is beneficial in various growing and hydroponic systems. pH Neutral: Clay pebbles are chemically inert and pH neutral, meaning they won't affect the acidity or alkalinity of the soil or water they come into contact with.