While wandering around the British Museum, I couldn't find a folding fan but stumbled upon a set of fixed fans from Korea.

Basically, they are made of thin bamboo splints and paper leaves.

The paper leaf stretched over a frame of a round, but what caught my attention was, the splaying shapes of the vein of the bamboo frame were bent almost in a 90 degrees angle.

The paper might be painted with tung oil, which is widely applied to umbrellas and fans in Asia.