The difference between the Low and High Pressure canisters is that one has 2% Propane and the other has 15% propane. Due to this propane content variation the amount of gas in the two canisters is also different. Low Pressure comes with 250 grams of Butane and High Pressure comes with 235 grams of Butane. The higher propane content allows for a higher discharge pressure which achieves a higher temperature required for Brazing purposes.