Fine white filamentous material reported falling during some sightings, in Europe and elsewhere, and repeatedly described as dissolving or sublimating within minutes of being handled. That property is why the material is evidentially frustrating: almost no sample has ever reached a laboratory intact, and the reports are therefore testimony about a substance rather than analysis of one.
It appears in the Fatima 1917 record as filaments that fell and melted away before they could be gathered, and it recurs in the twentieth-century sighting literature often enough that Jacques Vallee treats it in The Invisible College as one of the physical constants running through cases separated by centuries, alongside the buzzing and the falling-leaf descent. Conventional explanations offered for individual falls include ballooning spider silk and industrial fibre, which account for some cases and are contested for others.
Its interest to the Control System Hypothesis is exactly its habit of vanishing: a physical trace that consistently fails to survive collection is the kind of evidence the thesis predicts, and also the kind that can never settle anything.
Connections
Fatima 1917 · Jacques Vallee · The Invisible College · Control System Hypothesis