These adjusters are made from premium lightweight silicone, that is soft, comfortable and durable. Our elastic stoppers come in black and white and can quickly and easily adjust the length of the elastic to custom fit any mask. Suitable for adults and kid size masks. To install, use a needle and thread, a small crochet hook or bobby pin. At either end of the adjuster there is a small and big opening. Please refer to the instructions here or on our FAQ page.