The AACHENER INSTITUT FÜR BAUSCHADENSFORSCHUNG UND ANGEWANDTE BAUPHYSIK published a report about warm flat roofs, insulated with mineral wool. The report describes a few cases, where humidity penetration into the mineral wool changed the properties of the mineral wool. I copied a few graphs from this public report into this post.
GLAPOR cellular glass involves only foaming of waste glass up to 800°C without adding binders later on. The resulting cellular glass is absolutely water and vapour tight and has a much higher compressive strength (800kPa) with a higher thermal conductivity (0.055 W/mK). As a consequence, replacing 12cm mineral wool needs 16cm GLAPOR cellular glass, available at 32€/m² for larger quantities.
Given the absolute water and vapour tightness (and so a stable thermal conductivity and compressive strength) of GLAPOR cellular glass at a comparable price, cellular glass has to be considered in cases where a certain compressive strength is needed or a risk of water penetration is present.