Our cord locks are made of premium silicone, they are soft but not easy to break, can be reused.
These cord buckles are great to make masks fit just right behind the ears and they are very comfortable. They are difficult to place with just your fingers. You really need needle or small crochet hook for easy threading, please check the picture to get the steps.
Just put the rope in, then slide the buckle and adjust the tightness to make your rope tight and safe.