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Polyurethane rigid foam systems for thermal insulation (Part 1)

Why to use polyurethane foam for insulation?

  • Polyurethane foam has the lowest thermal conductivity factor λ (lamda) compared to any other insulating material (e.g. mineral wool, expanded or extruded polystyrene, etc)
  • This leads to the lowest possible insulation thickness for a given thermal resistance and, therefore, to savings, in terms of material quantity and insulation volume.
  • It is also the only kind of insulation that can be applied on site (in situ), ensuring uniform thermal insulation without thermal bridges.

What is polyurethane foam ?  

  • Polyurethane foam is a thermoset plastic cellular material
  • It consists of  polymer cell walls with gas inside them
  • Insulation properties are defined by :
    • Nature of the cell gas ( = the blowing agent used)
    • Closed cell content
    • Cell size
    • Cell wall thickness ( = foam density*)

*at a density of 40kg/m3, the solid polymer material makes up only 4% of total volume. 


What about blowing agents ?
Chemical blowing agents
A small part of the polyol blend (usually water) reacts with the isocyanate to produce gas (usually carbon dioxide : CO 2 )

Physical blowing agents
Blowing agent (a low boiling solvent) is dissolved in the polyol blend. Only polyol/water reacts with the isocyanate. Due to this reaction exotherm, blowing agent evaporates and fills/expands foam cells.
Such blowing agents are :
– Several fluorocarbons pre-blended in the polyol, like HFOs
– Hydrocarbons added in the polyol during manufacturing, like pentane isomers.

(to be continued)