All developed countries have to organize the phase out of HCFCs by the beginning of 2003. Only a few applications such as spray-, blockand PIR-foams can use HCFCs until the end of 2003. In some countries the use of HCFCs is already limited by national regulations. In Europe, household appliances have been produced for 10 years without the use of HCFCs. Manufacturers have gained considerable experience in the handling and processing of hydrocarbon blown foams during this time. Similarly, intensive investigations during the last year with HFC245fa has also generated significant data. Therefore we would like to compare the most attractive (environment friendly) alternative hydrocarbons and HFC245fa in this paper. The lower gas thermal conductivity of HFC245fa in comparison to Cyclopentane gives lower K-value foams. The difference in thermal conductivity is caused by the different concentrations of blowing agents