You really ought to be going up to a very fine wire wool or super-fine abrasive when you get close to the last coats. When I'm French polishing (and you CAN use water-based polyurethane with that technique) I use unprinted news-sheet as my final abrasive
- it doesn't get much finer than that. I'm not a specialist French polisher but it's quite easy to get a super-smooth glassy gloss finish (or paper-fine with matt) by wiping varnish through a cotton cloth.

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