Seems to be made with metal (buckle and clip), plastic (tension keeper), and a sturdy nylon material.Easily fits into my car's seat belt buckle. My 60ish pound dog has not been able to unbuckle it, and she seems to be more comfortable with this than with her seatbelt harness. She now tends to lay down easier (I prefer her laying than trying to walk around while we're driving up the winding mountain roads), not being pulled towards the seat back by the seat belt, like before.I now use the seatbelt harness, with this product, for a little piece of mind. I felt it would be safer for her harnessed self to be in an potential accident, than her being in a collar and choked/whiplashed.My mom also tried this with her Chihuahua mix (about 7lbs). While my mom shortened the product, her dog did not seem comfortable. She seems to prefer a smaller space, so she has less opportunity to slide all over the place.