The 9oz Insulated Kiki infant bottle is 100% plastic-free, environmentally progressive, and adapts to the needs of your growing child. Both the bottle and collar are crafted from safe, high grade #304 stainless steel. The included Natural Vent Nipple features a one-piece anti colic venting tube that stabilizes pressure in the bottle for continual feeding and a wide shape for a more natural latch. Each bottle has pressed internal volume marks that can be clearly viewed on the inside of the bottle for easy measuring. All bottles are compatible with silicone components from Pura including Natural Vent Nipples in various flow rates, silicone XL Sipper Spout, Silicone Straw, sealing disks, and sport top. The bottle is also compatible with nipples and spouts from other brands. This insulated bottle keeps liquids warm or cool for up to 6 hours. Bottle and nipples are BPA-free and will not leach toxins like plastic bottles and rings.