In Superman #11 the cover reads:
Now I know covers have a tendency to be a little... misrepresentative of what is actually contained in the issue, but I've read the issue twice. There doesn't seem to be any secret about it.
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I hate to break it to you, but the secret of the suit is:
This is an amazing upgrade for the Man of Steel. It only took him twenty six years before he could do the same thing Spider-Man did after the Secret Wars with his black costume.
Robot Chicken did enjoy themselves with this bit as well: What happens to Superman clothes while he's out "saving lives?"