Mineral wool is a fiber insulation made from natural materials, similar to fiberglass but not from glass.
R-Value measures insulation’s ability to resist heat flow, with higher R-Values indicating better thermal performance.
To install insulation in a crawl space, cover the vent openings with crawl space vent covers, seal the rim joists with rigid foam board insulation, and use foam sealant to seal gaps between the crawl space wall and sill.