I sweat a ton when I'm riding or running and don't have run out of dry areas to wipe sweat. I'm curious if you've used either of these and if it's worth buying.
i use headsweats/brooks hats for running, and for biking i have bondi bands that i wear under my helmet, although i've also used an under armour skull cap which works really well
I've worn a skull cap for the bike. My current weapon of choice is a sweat band (somewhat like a bondi band) under the helmet for the bike. It doesn't prevent 100% of the sweat from dripping into your eyes during super hot days but it does a great job of it. I think that they are more than worth it especially if you are training for long distance in hot weather.
If it means anything ... I lead a weekly bike ride group for DCTri every summer that goes between 60-100 miles. In that group, I would say that half of the people have some kind of sweat wicking contraptions on their heads underneath their helmets.
Just get a sweat band they sell at pretty much every bike shop. They're thin and go under the helmet. I've almost been blinded by my own beer soaked sweat on a few hot day bike rides, and that's not good when riding in traffic or anytime on a bike. Like acid in the eyeballs...it hurts!
As for running, I'd say 90% of the Triathletes out there use head sweats visors of some sort for the run.
Halo headbands work pretty well. They don't stop all of the sweat but they will reduce the amount that gets in your eyes by about 90%. They are thin enough to wear under a bike helmet. You'll get the best results if you wear the headband low on your forehead, so that the rubberized strip on the inside sits about 1/4" above your eyebrows.
On the run, you could wear a running cap or visor. Halo has a cap with the same rubberized band as found on the fabric headband. Most running shoe companies sell running caps made of moisture-wicking synthetic material: Asics, Mizuno, Nike, etc.
Ditto for the plug for Halo headbands/visors/caps. They work really well!
By the way, if you look really closely at my avatar photo, you can see me wearing a navy blue Halo headband under my bike helmet.
The only minor negative is that your head will stay a little hotter when running on hot days. Sometimes I'll fold the top part of the headband down for a few minutes to get some airflow onto my forehead.
I really appreciate it.