In a benchmarking of thermal insulation materials, it is easily demonstrated that the perfect thermal insulation does not exist:

• PIR, PUR, XPS and EPS are polymers and in that way combustible.
• Mineral wool cannot carry a high compressive load, not even at high density.
• Cellular glass has not a very low thermal conductivity, which can be compensated by thickness.
• Cellular glass, directly foamed from waste glass has the best ecologic balance and the polymer foams are at the other side.

One approach is by lobbying increasing the weight of the weak point of the competition in order to hide the own weak point. This was the very costly method of the past paid by all the customers for thermal insulation. Much more constructive is a combination with another thermal insulation to eliminate the own weak point.

In some cases, a passive flat roof is requested without any risk of fire transport during reparation of the roof. A large thickness of mineral wool is a possibility but rather high densities are needed. On top of that, free natural convection is not excluded with low temperatures outside. Cellular glass may have an even larger thickness to compensate the larger thermal conductivity. Polymer foams are out of the question due to their built-in combustibility.

In Denmark, Kingspan decided to collaborate and has choosen GLAPOR cellular glass as the top layer. Indeed, Kingspan PIR thermal insulation is giving the largest thermal resistance while GLAPOR cellular glass takes care about fire resistance and also delivers a hard protective surface under the water proofing membrane. The system assumes  a high quality vapour screen on the concrete to avoid humidity problems in the PIR. 

The combination guarantees the requested U-value, fire resistance and walkability of the flat roof. The thickness and weight of the roof remains below an acceptable limit. The solution will have a large life time and a nice (but not the best) ecology balance. At the end, the solution has an interesting price because GLAPOR cellular glass, directly foamed from waste glass is used. More information can be obtained by Celleglasplader in Denmark.