I wear a waxed cotton hat or a barret. I decided not to put any important stuff in there. The items would have to be small soft and resistant against sweat. Sweat, tallow and hair would stick to the stuff. This would require frequent cleaning or be very unhygenic. Itīs just not worth the hassle.
Just in case you wonder: Yes Itried it and was less than satisfied before I made this decision.
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If it isnīt broken, it doesnīt have enough features yet.