Metal foil beads are made with a thin layer of gold or silver leaf or foil sandwiched between two layers of clear glass. The first glass layer is usually drawn or wound, while the second layer of glass is folded around the metal leaf. Gold foil beads are more commonly found (archaeologically speaking) in Asia, while silver foil beads are more commonly found in European archaeological contexts.
There’s debate about where this type of bead originated. Some scholars say it was Egypt , others say it was India. Still others argue for Roman origins. The beads themselves are found all over Europe and Asia in various forms, and the majority of examples I’ve seen date between 100 BC and AD 1300.
Metal foil beads did differ between regions. I already mentioned that gold foil was more prevalent in Asia, while silver foil seems more common in Europe. That doesn’t mean that gold foil beads weren’t found in Europe or silver foil in Asia – they were, and they are. European groups (particularly the Norse) also had silver foil beads made with an inner layer of clear glass and an outer layer of cobalt blue glass. You can see some in the photo from Cnip. The equivalent would be any silver-lined dark blue glass beads you can find in stores today, though the Norse beads were about 5mm in diameter and usually 2, 3, or even 4 segments.
Metal foil beads tend to be segmented, which means that they were made by rolling the tube of glass over a mold that made it look like lots of beads stuck together. The bead maker then sliced the tube into beads with as many segments as s/he wanted, from 1 to as many as six. There could theoretically be beads with more segments, but I haven’t really seen examples of it.
But foil beads aren’t always segmented; they can be collared or gadrooned, too. Also, segmented beads can be single segments, not just double, triple, etc. Metal foil beads can really take any form, so long as there is a layer of foil in between two layers of glass.