Pat Evans
The commercial coasters we have are too small for my beer mugs and most of our drink glasses. They are also impervious to water which means when glasses sweat, they sit in a pool of water then drip when you pick them up. I made coasters from squares of carpet tiles which work great, but aren't that attractive.

I've resawn some cedar, walnut, and cherry for my BIL. Not long enough for pieces for furniture, but plenty to turn some wooden coaster. (He has the lathe, not me.)

I don't want a waterproof finish since I want the wood to absorb condensation. I'll put either feet or a waterproof backing on the bottom. Would BLO be a good choice for finish? Are wooden coasters even a viable idea? They might not last for years, but should be simple enough to make that they could be replaced frequently.