How thick with foam glass to get a satisfactory insulation value? Have received varying suggestions from 0.3 to 0.6. Grateful for help :)

[Ellenjustine]

Hello, we have moisture issues in the kitchen, where we have a crawl space. The plan is to tear up, clean out, and then possibly lay foam glass, geotextile, and then cast. How thick does the foam glass need to be, I have read anywhere from 0.3-0.6.
We don't plan to add any additional insulation.
The other option is to lay gravel, EPS, and then cast.

Tips and advice - gladly received.

Thank you in advance!