If you’ve got a well ventilated helmet then a Buff thing should work. they wick away the sweat from your head and help it evaporate away, which also keeps your head cool. If your buff is getting saturated and leaking sweat, then your helmet is not ventilating well enough for the evaporation process to work.
I always ride with my buff on – keeps my head warm in the winter, cool in the summer and keeps the sweat off my face and out of my eyes.
I forgot my buff a few rides ago and it was horrible. A wet sweaty head, dripping into my eyes and when I stopped my head chilled down. Horrible. I always buff up.