Aldi are currently slinging "airtight multilayer foil insulation designed by SuperFOIL with the DIY customer in mind"     According to the SF6 data sheet its Water Vapour Resistance is 1200MNs/g which makes it vapour tight in addition to being airtight. I understood that this was a no-no in the kind of application they're pushing here?  WIth an R-value of just 1.9 that's going to be a cold surface for vapour to condense on. Am I missing something?