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Angel hair or siliceous cotton is a sticky, fibrous substance reported in connection with UFO sightings, or manifestations of the Virgin Mary. It has been described as being like a cobweb or a jelly.
It is named for its similarity to fine hair, or spider webs, and in some cases the substance has been found to be the web threads of migrating spiders. Reports of angel hair say that it disintegrates or evaporates within a short time of forming. Angel hair is an important aspect of the UFO religion Raëlism, and one theory among ufologists is that it is created from "ionized air sleeting off an electromagnetic field" that surrounds a UFO.
There have been many reports of falls of angel hair around the world.
On October 27, 1954, Gennaro Lucetti and Pietro Lastrucci stood on the balcony of a hotel in St. Mark's Square in Venice and saw two "shining spindles" flying across the sky leaving a trail of the angel hair.
In the Portuguese city of Évora on November 2, 1959, angel hair was collected and analyzed under a microscope by a local school director and later by armed forces technicians and scientists of the University of Lisbon. The scientists concluded that the angel hair was produced by a small insect or perhaps some kind of single-celled organism.
In New Zealand and Australia local newspapers have reported many sightings since the 1950s, although many have been identified as spider webs after analysis.
The most recent incidence reported in Polonnaruwa, Sri Lanka on October 20, 2014. 
Explanations based on known phenomena include:
Non-scientific explanations based on beliefs regarding Unidentified Flying Objects include:
"Angel grass" is a related phenomenon. It is when short metallic threads fall from the sky, often forming intertwined loose masses. They are a type of Chaff, a radar counter-measure which can be in the form of fine strands, which is dropped by some military aircraft. It can also come from sounding rockets and balloons, which would have released it at high altitude for radar tracking.
... Angel hair has likewise been reported at sightings of the Virgin Mary, ...
these mysterious "webs" are associated with UFO sightings as well as angel sightings. Those who believe in UFOs believe the white filamentlike threads are related to the source that powers UFOs, while skeptics believe the filaments come from balloon spiders or a related spider family
A cobweb-like and jellylike substance which is also slightly radioactive often falls to the ground shortly after UFO sightings. The substance dubbed “angel’s hair” evaporates without a trace several hours after the sighting. The “hair” was reported to either disintegrate or turn into cottony tufts with an offensive smell when held in the hand. American ufologists refer to the material as “angel’s hair”; Italians call it “siliceous cotton”; and the French use the term “the Madonna’s present” to describe semitransparent threads that fall from heavens.
Angel hair is a rare phenomenon associated with UFO sightings, and the most famous incidence occurred in France in 1952. People of the town of Oloron were ... Suddenly someone cried, "What is that falling from the sky?" Great flakes were falling from a near cloudless sky. They seemed to be made of a cottony ...
Chitchat at the 22nd annual gathering of the Mutual UFO Network included discussions of mysterious angel hair left behind by UFOs
In ufology, this material is known as "angel hair," and some suspect that it is ionized air sleeting off an electromagnetic field surrounding a UFO. ...
(...) While Lynphiids are the principal gossamer spiders of England and other parts of the Northern hemisphere, they are certainly not responsible for all the notable falls of gossamer in Australia which are caused by a variety of native species in addition to introduced members of the Linyphiidae (...)
In other words, angel air may be the product of an electrostatic precipitation of atmospheric dust. This tangibly supports the view that UFOs are a ...
... create heavy atoms that react in ordinary air to produce a kind of precipitate that falls to the ground and disappears as the ionization decreases.