Chemtronics uses 2 types of flux: Soder-Wick and Chem-Wik lines use natural gum rosin. Per J-STD-004 Section 3.2, they are classified as ROL0. Per British Std. EN 29454-1:1993 and ISO9454-1:1990, they have a classification of 1.1.1.B. No-Clean and Lead-Free fluxes are synthetic (non-colophony)flux. Per J-STD-004 Section 3.2, they are classified as REL0. Per British Std. EN 29454-1:1993 and ISO9454-1:1990, the No-Clean and Lead-Free fluxes have a classification of 1.2.3.B.