Before you buy a head band, skull cap, or anything. Try what might be in your kitchen (not olive oil). I use Kleenex Viva absorbent towel.

Kleenex Viva Choose-A-Size Towels, 6 ct - Walmart.com

Its very absorbent, light weight, probably thinner than a head band, can be folded over or doubled up for extra absorbency, can act as a paper towel in case of a unscheduled pit stop, allows helmet vents to do their job, etc.

Price is right and it just might be in your kitchen right now, absorbing the stuff on the counter tops.

On some rides, when the temps are high or the humidity high, its easy to swap out the towel and insert another one.

In some of these fancy schmancy restaurants or hotels, the bathrooms have these paper towels that seem to cost like a buck a piece. I was tempted to get one of those and compare it with the Kleenex Viva for the sweat thing. Not done that yet.