The Aspiration Zero is not a metal credit card, as it is made of plastic like most other credit cards. There's no functional difference between a plastic card like the Aspiration Zero Card and a metal credit card, though, so don't dismiss the Aspiration Zero Card just because it isn't metal. If you like the card's terms and benefits, you should still consider applying.
Metal credit cards are usually expensive luxury cards. Some popular examples of metal credit cards are the Capital One Venture Rewards Credit Card, Chase Sapphire Preferred Card and American Express Gold Card.