The Stylish Keen uses a leather strap with a buckle made of steel and aluminum.  The Sporty strap is made of silicone and its pegs are made of aluminum.  The screws that hold the main gray plastic Keen unit together are coated in nickel.  In our Stylish Keen, the screws are sunk in so they do not touch the skin.  And in our Sporty Keen, the screws are sunk in and the silicone strap covers up the screw holes, so there would not be any skin contact.