As far as I know no they are not but its irrelevant anyway because if the letter gets scanned its gone because the scanners detect any organic matter. Any attempts to shield the contents from the scanner also guarantees it will be opened etc as it is a massive red flag. I had one order seized and when I contacted the vendor and when they described their packaging I wasn't surprised as they were attempting to use carbon paper. They might as well have sellotaped the drugs to the outside of the package.