Microfiber. Random selection of types and colours mainly inherited from the household - those used for finishing are replaced pretty frequently as they collect wax/polish.
SWMBO banned them from the washing machine as the smell and long term beading effect inside the drum is unwanted. To say the least.
Best ones I've found are the yellow multi pack ones from Costco, brilliant and a multitude of uses, wash separately and don't use fabric conditioner. I still prefer simple white cotton cloths for all metal polishing though, again the Costco multi pack ones are just brilliant