Gold Label Hydrocorn (clay pebbles) are manufactured using a mix of the best quality pure clays and are baked in an open furnace using high grade clean fuels, guaranteeing the absence of heavy metals or other contaminates.Gold Label Hydrocorn proudly carries the RHP for horticulture quality certificate.Gold Label Hydrocorn is the inert hydroponics substrate of choice for professionals. The 8-16 mm size provides stability and the unique uneven shape of the pebble is an ideal surface for roots and beneficial bacteria. The porous structure has a high water capacity and is suitable for both ebb/flood and top irrigation systems. Gold Label Hydrocorn is also available in 4-8mm and 16-25mm.