These skull face mask coverings, are made out of a semi rigid resin, to not only allow for flexibility and comfort. But also has the hard rigid feeling of real bone. All you need to do is feed the strings of your preferred face mask through the pre cut slits on the side. And then put it on as you would any other face mask. Skull mask comes in two sizes. so make sure before ordering that you measure your face. (from the tip of your nose to back of your jaw) for the right size. Medium 3 - 5 inches. and large is 5 1/2 - 7 inches. Mask come in various colors as well. Bone white, grey, jungle green, crimson red, and black.