Vacuum cellular glass is the holy grail of the thermal insulation world. Indeed, this thermal insulation should have a thermal conductivity of 0.021 W/mK, non-combustible, vapour tight, water tight and has rather larger compressive strength. But up to now, nobody found the holy grail …

Nevertheless Dr. Kaufmann, IfL Ingenieurbüro für Leichtbau GmbH & Co. KG,
09113 Chemnitz, Germany took a patentapplication on this subject. The patent makes a reference to another patent about VIP thermal insulation.

Dr. Kaufmann seems to be inspired by this type of thermal insulation, which has a very low thermal conductivity below 0.010 W/mK but is known to be easily damaged. With cellular glass, it is expected to get a much more robust type of  VIP.

The patent describes how the sandwich should look but without a description how to produce. A open celled foam should be sealed with a glass layer or a foamed glass layer or a polymer layer or a combination. The open cell kernel should be evacuated to get the very low thermal conductivity before sealing. Another option is to fill the open cell kernel with a noble gas.

We have the following comments on this patent application:

• Today, nobody has a low density recept for open cells except opening a closed cell  foam with a hydrostatic pressure. Higher density foams have a higher thermal conductivity through the glass matrix, compensating the benefit of a vacuum.
• The thermal conductivity of air or another gas drops at a pressure of 0.1 mbar, which is a vacuum difficult to maintain without pumping. Sealing with a polymer material in this case is not possible because the diffusion of most gases in the air is way too large.
• Sealing with glass or cellular glass on cellular glass without heating is today an unknown technology.

Today, this patent cannot be realized industrially and the obtained thermal insulation will never have a thermal conductivity below 0.020 W/mK (of the order of conventional PIR).