The heat shield that needed to be developed consists of five layers of a special material called Kapton. The outer layer, which will be the only one to face direct sunlight, is 0.05 millimeters thick, the other four are twice as thin, approximately the thickness of a human hair. They will protect scientific instruments from the sun’s heat.
This is a crucial step. According to NASA, it is possible that a total of 344 individual steps may fail before the telescope is launched – the successful unpacking of the heat shield means that 75 percent of them have been prevented and now there are “only” 86 left.