All "bottled in bond" bourbon is 100 proof. Some higher-proof bottlings are marketed as "barrel proof" or "cask strength", meaning they have not been diluted or have been only slightly diluted (less than 1% ABV dilution) after removal from the barrels. Bourbon whiskey may be sold at less than 80 proof but must be labeled as "diluted bourbon". A very small number of bourbon bottlings have been released with exceptionally high proof, sometimes exceeding 140 proof (70% ABV). In the mid-2010s, some sources began referring to these as "hazmat" bourbons, alluding to the ban in the U.S. Code of Federal Regulations on air travel passengers and crew members carrying such high-proof beverages due to their highly flammable nature. Such high proof levels are very uncommon even among "barrel proof" bourbons, as bourbon must enter the barrel at no higher than 125 proof and thus can only reach higher concentrations by disproportionate evaporation of water in the Angel's share during aging. Although only the focus of special attention for bourbon since the mid-2010s, very-high-proof products are not especially novel in general, as evidenced by the well-known Bacardi 151 brand of rum, which was available on the U.S. and Canadian markets from about 1963 until 2016 and was bottled at 75.5% ABV.
All "bottled in bond" bourbon is 100 proof. Some higher-proof bottlings are marketed as "barrel proof" or "cask strength", meaning they have not been diluted or have been only slightly diluted (less than 1% ABV dilution) after removal from the barrels. Bourbon whiskey may be sold at less than 80 proof but must be labeled as "diluted bourbon". A very small number of bourbon bottlings have been released with exceptionally high proof, sometimes exceeding 140 proof (70% ABV). In the mid-2010s, some sources began referring to these as "hazmat" bourbons, alluding to the ban in the U.S. Code of Federal Regulations on air travel passengers and crew members carrying such high-proof beverages due to their highly flammable nature. Such high proof levels are very uncommon even among "barrel proof" bourbons, as bourbon must enter the barrel at no higher than 125 proof and thus can only reach higher concentrations by disproportionate evaporation of water in the Angel's share during aging. Although only the focus of special attention for bourbon since the mid-2010s, very-high-proof products are not especially novel in general, as evidenced by the well-known Bacardi 151 brand of rum, which was available on the U.S. and Canadian markets from about 1963 until 2016 and was bottled at 75.5% ABV.