Topic "What vapor retarder over sealed crawl space?" a message from fstamm7

I am getting conflicting answers, so I hope you can help me out.

I am about to install 1600 sqf of solid, prefinished maple over a sealed and actively dehumidifier crawl space. Subfloor is plywood.

What vapor retarder should be used?

Any harm in using an impermeable retarder?

Thanks! Tony