D'Addario are American therefore spell "fibre" wrong. Nonetheless, here's what they have to say!

"The D'Addario Micro-fiber Polishing Cloth is a long-lasting cleaning cloth for all instruments that can be used with or without polishes. The Micro-fiber Cloth traps particles deep inside its fibers which are 2000 times finer than a human hair. This eliminates the need for harsh cleansers. D'Addario micro-fiber cloths last considerably longer than ordinary cloths and can be washed multiple times for lasting, repeatable performance you can rely on."