Stone wool is a vapor permeable insulation which allows water vapor to travel freely through it. This has important implications on building envelope durability: vapor diffusion is an important drying mechanism in wall assemblies and, as such, should be encouraged where possible. Many insulation materials are vapor impermeable and when poorly installed can lead to the "double vapor barrier phenomenon" trapped wall moisture between vapor impermeable insulation and an interior vapor barrier, commonly polyethylene. ROCKWOOL stone wool mitigates this issue by allowing free movement of water vapor, which removes incidental moisture from the wall assembly.

Stone wool is resistant to water infiltration; therefore bulk water that contacts the outer surface of the insulation will largely drain away and will not be absorbed. When moisture exposure is unavoidable, stone wool will not support mold and fungal growth as it is manufactured out of inorganic material. This makes it an ideal product for applications where moisture exposure is common such as basements, foundation walls, and under-slabs.