N-Butane, also known as normal butane, is medical grade butane and does not have the sulfur smell commonly found in butane camping tanks. N-Butane is the preferred solvent for most BHO extraction systems because of it’s low pressure during operation. N-Butane has a significantly lower vapor pressure curve than propane. This means that if butane and propane are at the same temperature, butane will be at a much lower pressure. The higher the pressure of the vapor inside the closed-loop extraction unit– the more dangerous operation of that extraction system becomes.