EcoFLEX rubber is made of vulcanized natural rubber, with up to 30% recycled material made of scrap from medical industry manufacturing such as rubber gloves, or stoppers. Although it uses recycled material, it is extremely durable due to the strong and flexible nature of vulcanized natural rubber. It is also super grippy (think pink eraser or a new shoe sole) and is our stiffest material making it a seamless transition to throwing rubber while still reducing ground-play. The PDGA approved Koi gives you the confidence needed to run even the most difficult putts and dangerous approaches.