There are 2 choices of gas to use in this system, either pure nitrogen (N2) or nitrous oxide (N2O).Pure nitrogen is flavourless and produces dense creamy head and cascading bubbles like a Guinness. However it takes longer or more shaking to dissolve into your drink before you can serve.Nitrous oxide has a very slight sweet flavour to it and produces the same effect with less time or shaking (virtually immediately). However it can produce a less attractive foam with larger bubbles if left too long.It's best to play around with both to find your favourite, you can also combine 1 bulb of one with one of the other.You can add either gas below