Just happened to stumble across this PDF from Oakridge on the net. It tests 4 different foams blown with different refrigerants etc. Interesting read and the conductivity goes up quite a bit in the first two years. The foam made with 141b is quite a bit better quality than the environmentally required replacements.
Just interesting to see how the different materials degrade with age etc.
http://web.ornl.gov/~webworks/cpr/pres/107629.pdf