straw has weighted ball so it will always moves to the liquidnSILIFLEX-straw technology, Valve-freenBPA and Phthalate freenBOT features an innovative straw technology that moves to the liquid whenever the cup is tilted allowing the child to sip to the last drop. The cup is designed with a simple integrated handle and lid to eliminate lost parts. The handle, lid, and base is made of polypropylene while the straw is made from food-grade silicone and a stainless steel weighted ball.