Zip file size

Why is the zip file (that is created when Archive is used), bigger than the total of all the zipped files?

How much bigger? A few bytes, or megabytes, or...?

What kind of files are they? If they're already compressed then zip won't usually be able to make them smaller.

What happens when you use any other zip tool? Is this specific to Opus?

They are just ordinary picture (*.jpg) files.
The resultant zip file is 224M against 210M unzipped.
Haven't tried another zip tool, as I don't think I have one.

JPG files are already compressed and won't compress any smaller when zipped.

Zip files have a small overhead to store things like the filenames and attributes as well as the actual file data.

14MB seems like a lot of extra but might make sense it is a huge number of small files.

I expect you'll see the same result if you try another tool.

I understand.
I was just trying to save some disk space!!