I wear one backwards under my helmet, it absorbs sweat and keeps it out of my eyes. Also the brim covers the back of my neck from the sun. I buy the cheapos from nashbar because they get pretty nasty after a few rides
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2010 Kestrel RT900SL, 800k carbon, chorus/record, speedplay, zonda
2000 litespeed Unicoi Ti, XTR,XT, Campy crank, time atac, carbon forks