Level Up To A Faster Nipple Flow! Dr. Brown’S Level 4 Narrow Nipple Is Our Fastest Flow Nipple For Babies 9M+. Dr. Brown’S Uniquely Designed Level 4 Narrow Nipple Is A Fast-Flow Nipple That Works Together With Our Internal Vent System To Help Growing Babies Feed At Their Own Pace. Each Level 4 Nipple Provides The Same Consistent Flow Rate, So Both You And Baby Know Exactly What To Expect. Together With The Anti-Colic Internal Vent System, The Level 4 Nipple Offers Vacuum-Free Feeding That Is Clinically Proven To Reduce Colic, Decreases Spit-Up, Burping And Gas, Better Preserves Nutrients, And Aids In Digestion For A Good Night’S Sleep. Made Of Super-Soft, High-Grade Silicone, The Level 4 Nipple Fits All Dr. Brown’S Narrow Bottles. The Suggested Age Range For The Level 4 Nipple Is 9 Months+, But Baby’S Preferred Flow Rate May Vary. Dishwasher (Top Rack) And Sterilizer Safe. Bpa Free. Included Is 2X Options+ Level 4 Narrow Nipples.