Snowboard jacket breathability is not something that the casual snowboarder usually thinks about, but it is important all the same. It is just as important, in fact, as the water proof rating. This is especially true for those who plan on spending long amounts of time on the mountain, say more than six hours. Before that point it is still important, but waterproof rating is more so. The short definition of breathability is the ability, or inability, of the jacket to absorb moisture from the air. The more moisture a jacket will absorb, the drier the person wearing it will stay. This is very important in the cold because moisture draws heat out of the body. The drier you are the warmer you are.
Snowboard jacket breathability is measured by the number of grams of moisture the jacket can absorb. So a jacket that can absorb 10,000 grams will be shown as a rating of 10K. In general, a good standard jacket will have a rating of 8k to 10k while an upper end higher quality jacket will have a rating closer to 20k. Of course the higher the breathability rating the higher the cost, so it is a good idea to determine what you really need in a jacket in terms of a breathability rating.
This can vary based on a number of factors such as humidity and how much time you spend snowboarding. If you only go a couple of times a year on vacation, and you only spend six hours or so on the mountain a day, you really do not need much more than a snowboard jacket breathability rating of 8k to 10k. However, if you are a professional snowboarder, or someone who gets to the mountain often, then you may want to invest in a higher quality jacket with a higher breathability rating.
It is also important to remember than that while snowboard jacket breathability is important, there are other factors that are just as important or more so to consider when buying a new jacket. Waterproof rating is very important as it tells how much ground water, such as melted snow, will be able to get through to your body. Fit is an extremely important factor as well. An ill-fitting jacket, whether too snug or too loose, will not keep you warm properly. The warmest jacket is going to have a good balance between all of these factors, and staying warm and dry while snowboarding are two very important to snowboarding safety.