Bierfilzl or "Beer Felt". The absolute best coasters. 5mm thick of best quality German felt, hand cut in the U.S. Quiet, absorbent (this felt can absorb 30% of its own weight in moisture before it feels wet) long lasting large enough for almost any glass or mug.
Priced and sold as a set of 4.
Many more colors typically in stock. OK for current availability.