NASA's Common Data Format, described at http://cdf.gsfc.nasa.gov/, is a binary format for storing self-describing data. It is typically used to store tabular data for subject areas like space and solar physics. Since v4.0-1 TOPCAT is capable of reading CDF files, though it can't write them. Currently, no attempt is made to represent values representing times in a human-friendly fashion. This may change in future releases.