The present study embraces measurements of insulation resistance on a number of types and makes of printed-circuit boards. The insulation measurements were performed on boards just received from the manufacturer, as well as on boards exposed to humidity or to elevated temperatures. A total of 33 types from five different material categories were obtained. The test material used thus originated from a variety of independent sources. The purpose of the project was to investigate the frequency with which batches with insufficiently baked material - and consequently having a poor insulation resistance - were encountered in practice. No such batches were in fact found, and it is likely that they do not occur as often as had previously been assumed.