Eyelash extensions can be made of various materials, including synthetic fibers, mink, silk, and human hair. Synthetic fibers are the most common material used for eyelash extensions because they are lightweight, durable, and hypoallergenic. Synthetic lashes can be made of different types of fibers, such as nylon, polyester, or PBT (polybutylene terephthalate). Mink and silk lashes are also popular options because they provide a more natural look and feel, but they are more expensive than synthetic lashes. Human hair lashes are another option, but they are less common and more expensive than synthetic lashes. Ultimately, the material used for eyelash extensions depends on personal preference, budget, and desired look.