I bought one of them at a flea market last week and now I wonder what I have been wearing around my neck. Anyone know what the bead like things that hold the water are? The one I have is a cloth tube which swells up when wet to about the size of a quarter and is about 20"long and then some so you can tie it if you want.
Most of them use silica gel. It’s commonly used as a dessicant - those little packs of things that soak up moisture from the air and have a “do not eat” label.