My guess is that they DO have a purpose. They are a barrier, they are VERY compact, and they are very inexpensive. But, in reality, I would bet it's because the marketers can say that their kits include a "NASA technology" BLANKET. What is more comforting to someone in a crises situation; the knowledge that the 72 hr. kit in their trunk contains a BLANKET (oooh) or a trash bag? I would make an exception for the SPACE bag. Those seem to do pretty well.<br><br>