When you heat glass enough to almost melt it, it becomes a
gooey, gluey substance,
like very stiff slime. In that condition, it's rolled flat to
make window-glass, or spun
on the end of a rod to make cups and bottles, or blown up like a
balloon to make
bottles with very thin necks.
Also when glass is in that condition, if you grab a little pinch
of it (with tongs!)
and slowly pull it away from the main glob, it stretches way out
and becomes
very thin before it finally breaks. It can be stretched to where
it almost has the
consistency of cotton candy or fine hair, and that's the
material used in
fiberglass home insulation. When it's stretched not quite as
thin as that, to the
thickness of a thick sewing thread or a nylon fishing line, it's
quite flexible, and
in this condition, a plastic jacket is formed over it, just like
a piece of wire, then
several of them are jacketed into a single cable and used for
"fiberoptic" data
communication ... a pulsed bright infrared light, injected into
one end with a
laser diode, travels very nicely through several miles of this
glass thread to be
received at the other end of the cable.
So "fiberglass" is glass that's been melted and stretched until
it's no thicker
than all those other things we've been calling "fiber" for
hundreds of years.
