I'm not sure exactly what it's made of, a man-made poly something I think. Very absorbent. To find them cheap look in the automotive section. There they are used for drying car. The can also be found as camping towel$$$$$, and in the spa section of BB&B as hair wraps. Also used for dish towels and dusting clothes.
I bought a huge bag of them from costco for less than $12, I think. It's been awhile. The best place to get them is janatorial supply stores. They are cheap and you can buy them individualy or in bulk.