Durable Tritan Plastic Construction: Made from BPA and phthalate-free Eastman Tritan plastic for long-lasting use. Secure Lid: Screw-on lid creates leak-proof seal to keep shaker cup contents clean. Patented Mixing System: 316 surgical-grade stainless steel wire whisk found only in BlenderBottle shaker cups. Easy Portability: Wide loop top allows for easy carrying or attaching keys. Complete Leak-Proof Seal: Secure flip cap with SpoutGuard keeps mouthpiece clean and leak-proof.