A round Chinese wealthy merchant, scholar or nobleman's skull cap.
Sometimes called Water Mellon caps on some sellers sites.
I wear this hat to play triad or oriental noble characters.
In the photo below I'am taking part in a larp based enter the dragon competition called Death Match.
(further photos at bottom of post)
This a fancy dress hat with a pre-attached pigtail of a style worn by Kwan Tak-hing in Enter the Dragon. Its made of cardboard then covered in fabric, their are similar fancy dress just made of fabric that sit uncomfortably on the head, this one is fine to wear.
The pigtail seems to have grown in modern copies of this hat from tassels that denoted ranks, often by expensive beads woven into the tassel or the number or colour of the tassels.
In this hat the tassel is much longer than it should be that why its more of a pig tail.