What environmental condition must be avoided when storing foamglas?

High humidity must be avoided when storing Foamglas because this type of insulation is highly porous and can absorb moisture. When Foamglas absorbs moisture, it may lose its insulative properties and effectiveness, potentially leading to structural issues in insulation applications. Protecting Foamglas from high humidity ensures that it maintains its performance characteristics and longevity.

Other options like direct sunlight, freezing temperatures, and damp areas also present risks, but the critical issue with moisture from high humidity stands out in terms of its direct impact on the material's integrity.