Obtained by the chemical reaction between two liquid components: isocyanate and polyhydroxy, in the presence of catalysts. The cellular structure is formed by the release of CO2 in a secondary chemical reaction or by the boiling of a liquid (blowing agent) under the effect of the heat of reaction.
In recent decades, polyurethane has attracted attention in the field of thermal insulation at low temperatures.
Its main characteristics are:
low thermal conductivity due to the replacement of air in the cells by a high molecular weight gas; possibility of being expanded at the place of employment;
high surface temperatures; and resist the mold and attack of various parasites.
The rigid foams, used for thermal insulation, have a relatively high proportion of closed cells, which further improves the insulation characteristic of this material. There are techniques for the manufacture of foams whose cells are all closed, practically watertight, vapors and gases.
