The term "angel hairs" refers to a peculiar substance sometime reported to have fallen or to be found, during or immediately after the observation of UFOs. Also known in Italy as "bambagia silicea" (siliceous cotton-wool), this substance has never been clearly and unequivocally defined. Though Italy is probably the country with most such cases in the world, given the small global number of reports, an international catalogue is also updated (more than 200 cases as yet), as well as an archive of all published references to the subject.