Planners and building owners often demand sandwich panels with a non-combustible mineral fiber core for more safety in case of fire.

Sandwich panels with a PUR rigid foam core also offer sufficient passive safety in the event of fire. Because these panels do not contribute to the spread of fire.

This means that the PUR rigid foam core is only destroyed where there is direct exposure to fire and high temperatures, e.g. by burning goods inside a hall.

Due to the lack of oxygen, however, no fire propagation takes place within the PUR sandwich elements, so that no danger to other parts of the building remote from the source of the fire can occur.

This extraordinarily positive behavior of PUR sandwich elements has been proven again and again by many practical fire tests and not least by occasional fires.

Therefore, sandwich panels with a non-combustible core of mineral fibers are only interesting if fire resistance classes are required by the authorities.

This means that if, for example, the fire resistance class W90 according to DIN 4102-3 is required in a building permit for an exterior wall, this requirement can be met with sandwich panels with a mineral fiber core.

If non-combustibility of the wall or roof elements (A1, A2) is required, the mineral fiber elements cannot be used either, since they are only flame-retardant (B1) according to DIN 4102-1, just like PUR sandwich panels, because of the combustible adhesives used to bond the mineral fiber core to the metal cover layers.

Generally it can be said that the ideal synergy materials for sandwich panels are a polyurethane rigid foam core and sheet steel cover layers, just as this system was once developed by Professor Dr. Jungbluth, Dr. Stamm and Dr. Witte.

  • In contrast to PUR sandwich panels, sandwich panels with a mineral core can easily absorb moisture and water.
  • Panels with a mineral core, for example, weigh about 18kg/m² with a thickness of 80mm compared to only 12.7kg/m² for a PUR sandwich element, i.e. they are about 40% heavier. This is important to know for the installation effort.
  • The mineral fiber core of sandwich panels usually has a thermal conductivity l of 0.040 or 0.045W/mK. Due to the closed-cell hard foam core and the vapour-tight cover layers, the PUR sandwich panel has a significantly better thermal conductivity of only 0.025W/mK, almost twice as good.


This results in a heat transfer coefficient U of 0.52W/m²K for an 80mm mineral fiber sandwich panel, whereas a U value of only 0.3W/m²K results for an 80mm PUR sandwich panel. This means approx. 40% less heat and energy loss than with mineral fiber panels.


  • However, due to the higher weight, the airborne sound insulation of sandwich panels with mineral wool is about 8dB better. In many industrial buildings, however, this is of only secondary importance, especially since noise in an industrial warehouse today must be avoided at source for occupational health and safety reasons.

Since, as everyone knows from their own experience, it is fortunately relatively seldom that there is a fire somewhere, the function of the building components for the building use should be considered in the building design, and PUR sandwich panels have the overall better properties compared to panels with a mineral fiber core.

Netphen, August 2002

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