Your Lifefactory Baby Bottle is there for the whole adventure, so Lifefactory offers nipples that fit the 4 oz and 9 oz Baby Bottles in four sizes: Stage 1, 0-3 months; Stage 2, 3-6 months; Stage 3, 6 months; and Y-cut nipples for the fastest flow of milk or formula. Made of silicone, BPS/BPA/phthalate free, and featuring a vented design, these nipples are made to take everyday adventures in stride.