Boxed Within

We are little creatures; all of us have different features. One of us in glass is set; one of us you'll find in jet. Another you may see in tin, and the fourth is boxed within . If the fifth you should pursue, it can never fly from you. What are we?
We are vowels.
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Boxed Within Riddle Meme.
Boxed Within Riddle Meme with riddle and answer page link.