There is no definitive answer to this question as it depends on a number of factors, including the specific carbon filter you are using and the application in which it will be used. However, in general, it is usually better to push air through a carbon filter rather than pull it. One reason for this is that when you pull air through a filter, the air has a tendency to bypass the filter media. This means that some of the contaminants in the air will not be removed by the filter. Another reason to push air through a carbon filter is that it can help to prevent clogging. When air is pulled through a filter, any particles that become trapped in the media can cause clogging. This can reduce the efficiency of the filter and eventually lead to it failing completely. If you are using a carbon filter in an application where air needs to be pulled through, such as in a fume hood, make sure to choose a filter with a high efficiency rating. This will help to ensure that the majority of contaminants are removed from the air.