Why Use Pentane, a Hydrocarbon?
Polyisocyanurate foams were traditionally produced using CFC-11 (a chloro-fluorocarbon) as the blowing agent. When evidence became irrefutable that CFCs destroyed stratospheric ozone, most of the world adopted the ground-breaking Montreal Protocol, which mandated the phaseout of CFCs for non-essential uses by 1996. Many polyiso producers gradually transitioned to HCFC-141b (a hydro-chlorofluorocarbon), which has only 10% to 12% the ozone-depletion potential of CFC-11. But since HCFC-141b was recognized as the most damaging of the HCFCs, HCFC-141b would be only a temporary solution. (Modifications to the Montreal Protocol later mandated the phaseout of this chemical by 2003.)
As polyiso manufacturers studied possible substitutes for HCFC-141b, two different hydrofluorocarbons emerged as possible substitutes: HFC-245FA and HFC-365. HFCs have the advantage of being non-ozone-depleting (since they don't contain chlorine or bromine), but they are significant greenhouse gases. Most HFCs are also expensive to manufacture.
Another alternative was a hydrocarbon blowing agent - - pentane. Hydrocarbon blowing agents have the advantage of being less expensive, but their flammability requires special safety measures at manufacturing plants. Yet the cured foam is no more flammable than HCFC-blown foam.
As for energy performance, leading industry experts report there is no appreciable change in R-value with the hydrocarbon-blown foams. The finer cell structure of pentane-blown foams, for instance, tends to offset the pentane's higher thermal conductivity. Pentane-blown foams have another advantage: better dimensional stability due to the fact that pentane does not condense as much as HCFC-141b at temperatures normally experienced by the foam in use. The condensation of HCFC-141b causes the cells to shrink and expand on a cyclical basis, reducing dimensional stability."