Thick nylon. The buckle is heavy and of good quality and holds the nylon tight enough not to have to be adjusted all day. The only negative I can say about these straps is that the end of the strap is cut and shot at an unusual angle to prevent unraveling. I wanted to trim it off because of a little excess that doesn't reach my nearest belt loop. I'm not sure how exactly I can do this with the corner already made. Very pretty otherwise.