Xenylon

Xenylon was an organic material created by processing a form of algae. s in the mid-2260s - early 2270s were made of xenylon.

In 2269, Spock noted that while a shrunken Nurse Christine Chapel's uniform fit her perfectly, her titanium bracelet was too big for her. He then surmised (correctly) that spiroid epsilon waves only caused organic material to shrink, as the crewmembers and their xenylon uniforms had both shrunk at the same rate, while metal objects, such as Chapel's bracelet, remained their normal size. 

Xenilon