I am looking at insulated underground pex for a 40' or so run from my boiler building to the house, and have come across two types of insulation that are used in the better quality products (not even considering the bubble wrapped products). Logstor and Thermopex (Central Boiler?) use polyurethane foam which has an r value of about 6 from what I can find out. The others, Micro-flex, Wirsbo (R-flex) and Heat Seal, use polyethylene foam, which seems to have an r value of only 3 or so....I need 1 1/2" ID which rules out the Thermopex. Logstor makes it but does not have the dual pipe available anywhere and I would have to $pecial order it....While my run is quite short, maybe the lower r value of the polyethylene insulation products won't matter much....I have considered foaming the lines in the trench but have high ground water and am not sold on that method yet....What say others?