The median employee in the Netherlands is just barely at the threshold of working full-time (defined as 35 hours or more). Few of those who work full-time cross 40 hours, and part-time can be well below 30; the average comes out to about 30.
Of those working part-time (less than 35 hours), about 12% would like to work more but has no suitable work available, so these are underemployed people working part-time.