gothamcity:

The Pacific Trust sent representatives to Disney with authentic textile samples that would have been present in ancient Polynesia. Two major materials, tapa and pandanus, are the basis for most costumes in the film.

“Because the materials are natural, they tend to be more structured than a fabric. How they move on people, and how they move when wet is different and it’s important to get those things right. For Moana’s costume I knew she was an adventurer, a voyager, and the costume had to reflect that. I added a slit to the front of her skirt, which ended up working technically as well. We work very closely to the animation department and the simulation team. Whatever outfit she wears needs to be historically correct, it needs to have materials that are accurate to the history, and it has to allow movement.” 

— NEYSA BOVÉ, COSTUME DESIGNER FOR MOANA (2016)