Read up on authentic fabrics, weaves and construction methods before you buy something that is pure fantasy.
If your character is a historic character, or their design is based on period costume, your choice of fabrics will be limited by the materials and methods that were available at the time. While I don’t think it is necessary to go all „authentic“ for something that is not a reenactment costume, I do use historic dress as a reference for cosplay. It helps me better understand the idea behind the design, how the construction works, and how to achieve a realistic look. The same is true if the design is based on ethnic dress, like a Japanese kimono. Read up on authentic fabrics, weaves and construction methods before you buy something that is pure fantasy.