Moss Clothing
Moss clothing is an old fashioned tradition seen on Sacaethea. It was popular until about five hundred years ago, during the worldwide depression that took place after the Burning Sea War.
Moss clothing isn't used anymore due to the clothing industry having bounced back in the last few hundred years. Nevertheless, some still choose to wear it on occasion, as either an effort to remember the struggles their ancestors went through, or just for the eccentricity.
Last Resort
Moss clothing became popular right after the Burning Sea War. Due to many resources main producers, such as clothing, clothes became much more expensive. Before the war, Stayc Ster was the planet's leading producer in clothing, and after the entire nation went up in flames new clothing became scarce.
Moss clothing became a temporary item of clothing, as it was harvested en masse from the bark of the plentiful grandia trees. The moss is tied onto thin, wide leaves to prevent water leaking through, and can be worn easily.
Sacaethean pirates don't wear much clothing anyways due to them being avids and having thick feathers, but they are not waterproof and if often rains on the islands they call home, which means clothing is used almost purely for water protection.
Such a fun take on the prompt! I never would have thought of clothing as something that could be a traditional or old fashioned behavior, but it really does fit. It is also really cool to hear about a time in your world’s history where fashions changed for a very specific change, that did not stick around once things settled.