Shown here is a very large foil-filled flashbulb, about the largest I've seen. I do not know a whole lot about these, but I have heard they were used by the military many decades ago, to take pictures from spy airplanes at night. I've also seen them used to take pictures of large, dark caves. There are smaller sizes of these bulbs too (see related links below). I believe the foil is magnesium foil.