3D Korean Silk Eyelash Extensions are made with a man-made plastic fiber called PBT - Polybutylene Terephthalate, a type of polyester that’s heated, machine-molded into desired lash shapes and set as it cools. They are commonly available and meant for disposal after single usage. Synthetic lashes tends to be thicker than human hair lashes, they have stubbier ends so there may be a contrast between your natural eyelashes and the synthetic falsies you apply on. They usually have a stiffer band to accommodate for thicker fibers, making them feel heavier on the eyes.