Small, fits perfect under helmet. Cover sweat really well - I only get drops of sweat on my face from super hot super long summer rides. It's great at getting sweat for probably 95% of my rides, but possible to sweat through it - probably the limitation of being super small.
I still have my other sweat band from PI, but this is a sweet improvement. Holds more sweat keeping a deluge of sweat off your helmet padding. This is important to me. Not to mention this thing is difficult to saturate to the point of dripping. Air passing through it provides cooling. I use it in the cooler part of the year to block some of the cold air on my head. I actually have their cooler weather one that partially covers my ears and its awesome also. Well, well, worth the money.
Logging long distance rides in the Florida heat and humidity has its side effects. The salty sweat spray on the inside of my eye wear makes for a distracting ride at times. Using this head band has drastically reduced the sweat from finding its way onto my lenses. Simple and effective solution.
I have a real problem with salt in my eyes when mountain biking. A whole head bandana works great when it's not too hot, but I still have some hair left (68 yo), so a lot of the season I need the air up there. This band really keeps the sweat out of my eyes and stays in place under my helmet.
Living in Hawaii on the rainy side of an island where humidity rules and sweat drips on my uphill climbs, I thought this might help, but it is a one-size fits all model and my head must be a no-size-fits model. Way too tight --headache tight. I stretched it by wrapping it around my bicycle seat and leaving it there for a week.Now, it works a little and still feels a rubber band.
For someone who sweats a lot, I do notice that the headband keeps most of the sweat of the backside of my lenses. I dont notice Im wearing it until I take my helmet off. Superior to a competitors brand that I also have.
Yay no more sweat in my eyes. I was skeptical but I was desperate so I got a headband and it works great l dont know why I didnt do it sooner so if you have the same problem get a headband.