Have noticed in the past that finding the Dow Blue Foam was becoming a problem. I went to about 17 Home Depots and Lowes and couldn't find it. I contacted Dow and they sell it to two different distributions companies that then sell it to Lowes and White Cap and others. The foam is the Dow 1/4 inch X 48 inches by 50 feet fan fold.
To order it go to the commercial desk in Lowes and tell them they can get it delivered by ordering it from Blue Linx Company. You can see it at bluelinxco.com in their catalog. It is Blue Linx catalog number 669153 and it is called Dow Fanfold Underlayment. You can't buy it directly from them but they deliver quickly to Lowes or others when you order it through them. Mine took about 5 days to get.
I won't say how many miles I drove or how many hours searching the internet to locate this stuff, but I finally did find it and have it to build my planes. Hope this helps someone.
I forgot to answer the 2nd question. From what I've read they are only putting plastic on one side now. Seems to be fine for the planes I build which are fun flyers and small combat planes. We do put some criss-cross tape on the wings to strengthen them. Hope that helps.
our lowes is now selling a brittle foam with plastic on both sides, they used to have the blue foam. on the other hand our home depot used to sell this same brittle stuff, but when lowes swapped, so did they, Now Home Depot sells the same thing as the DOW blue foam was, but now it is pink, from owens corning.