The Pura Kiki infant bottle features a food grade stainless steel bottle (18/8), medical grade silicone components, and zero plastic parts! 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 our natural vent nipples in various flow rates, silicone xl sipper spout, silicone straw, big mouth sport top, and sealing disks. Bottles may be used for storing breast milk in the freezer by following the instructions included with each bottle. The bottle is also compatible with nipples and spouts from other brands. With Pura you can rest assured that you are always using the safest and most eco-progressive bottle on the market. One life. One bottle.