I didn't notice this before, but all decriptions of a folder are gone after archiving (7z, ZIP, rar)
& unpacking again.
For filetypes like MP3 or JPG where the description can be stored inside the file format's own metadata, the descriptions will be preserved in archives (since they are in the files themselves).
In other cases, like descriptions on folders or on plain text files, where the descriptions have to be stored as separate NTFS metadata, they will be lost if you copy/move the files to a non-NTFS drive or into an archive.
Well, actually i created that archive on a NTFS drive, so the description should stay present after unpacking. 
That only helps if you put a description on the archive itself.
The insides of the archive are not an NTFS drive, even if the archive is stored on one.
Ok, that's how you meant it. I wasn't aware, that data inside archives lose their NTFS status permanently, but it sounds logical now.
Then i will archive only the contents of the folder, keeping the folder (& descriptions) above. Thank you!