I got the wide version. The material is 65% cotton and 35% spandex. It is very stretchable like a sock and constructed like a tube with the ends joined together. There is a 2 3/8 inch zippered opening for acces to the inside of the tube. The unstretched state is 4 3/8 inches long and 3 inches wide. If you sweat a lot, whatever you put inside will get wet. Works well for holding keys and other small objects.
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