A Buff is basically a tube of stretchy, breathable fabric you can wear around the head, face and neck in a variety of permutations. Beanie, bandana, sweat band, scarf, balaclava and pirate hat for starters. There are other manufacturers but, like vacuum cleaners are all called Hoovers, they are called Buffs.
I always used to think Buffs (sometimes called a Snood if you are old-school) were a bit of an affectation until I went to Prague in the middle of winter a few years back. The warmest temperature while I was there was -16C and I really needed to keep my face covered. I bought a thermal Buff which is like all other Buffs but has one third made out of a fleece material. I have to say it did the job brilliantly – no more frozen face, no ice-cold nose, etc.
Since then I purchased a standard Buff for general use and I was given one designed for hot temperatures to maximise cooling. Now I’d say they are just about the most useful bit of kit that can be carried when you’re hiking-instant sunshield, instant warmth and a Buff can even double as a towel. Thoroughly recommended as multifunctional, ultralight and pack down to a very small size that will fit in any bergen.
Pictures speak louder than words so here is a link to YouTube via Buff’s website showing how to wear a Buff