Gold (HH): super-high friction, high heat (longer lasting) sintered bronze metallic compound with diamond ground surface for wet/extreme conditions (due to high heat generation, HH-Gold compound is not for Hydraulic/DH race use unless OE specified). Red (R): high friction, low heat (faster wearing) Kevlar based, semi-metallic soft compound for DH racing. Green: med-high friction (medium wearing) Kevlar based, organic compound for XC/all-purpose (no squeal).