Like all Hydro Flask caps, the Hydro Flip is made out of 100% recyclable PP5 and is BPA-free. The lid features a flip-top opening with rubber stopper to plug the opening and help prevent spills when not in use. Hydro Flask is now offering Hydro Flip Lids in four new colors along with the original black. The colored flip lids are a perfect opportunity to personalize your Wide Mouth Hydro Flask. New colors include Electric Blue, Banana Yellow, Limeade and Perfect Purple. The Hydro Flip lid fits our 18 oz Wide Mouth, 40 oz and 64 oz flasks. Please note that the Hydro Flip lid does not fit on the older style Wide Mouth flasks. To find out which style flask you have and whether the Hydro Flip will fit yours, check out the Hydro Flip Fit Guide. Please note that the Hydro Flip Lid is not leak proof.