The Flow Cap from CAYL is made of a breathable and stretchy Polyester and Spandex mix fabric with a DWR finish. This unique fabric has tiny grid pattern perforations that aid air flow (hence the name). It's super lightweight nature makes it great for running or lightweight hiking. The coolmax headband helps wick away moisture and keep you cool. One size fits most due to the adjustable bungee cord fastener that is reflective too and there is a reflective CAYL logo to the back side and hanging tab to the rear. One size fits most.