In a message dated 4/25/2006 10:25:03 A.M. Eastern Standard Time, [log in to unmask] writes: I agree--closed cell won't breathe so it serves as a moisture barrier. Make sure you know where your dew point will be (where in the wall condensation will occur) to avoid letting moisture come in contact with wood or concrete In my former capacity, we always insisted that backer rod for caulking be closed-cell polyurethane foam, because outgassing from the open-cell stuff had been found to percolate out through the sealant and ruin it. Why isn't there going to be some deleterious effect (on paint?) of open-cell polyurethane insulation? Seems to me there's an inconsistency between Bruce wanting open-cell polyurethane insulation and me wanting closed-cell backer rod. Or am I missing something? Ralph -- To terminate puerile preservation prattling among pals and the uncoffee-ed, or to change your settings, go to: <http://listserv.icors.org/archives/bullamanka-pinheads.html>