We found a paper about gravel with focus on the hygrothermal properties, written by the “Norwegian Building Research Institute” inTrondheim. The measurements are performed on foamed glass gravel Hasopor produced in Norway.

• Thermal conductivity and resistance are given inclusive water absorption.
• Mechanical properties including long term creep behaviour are described
• Long term water absorption and capillary effect are given.
• Reistance to freezing and thawing

The conclusion of the report is clear:

Measurements of various hygrothermal and mechanical properties for granulated cellular glass have been presented. Granulated cellular glass is suitable for the use as thermal and frost insulating layer, water capillary barrier, drainage layer and light fill for in ground constructions.

Even under complete immersion after a long time, the thermal conductivity only doubles like shown herunder.