Dr. Brown s Polypropylene 2-Bottle Sampler Kit features a patented internal vent system that eliminates the vacuum and air bubbles to help reduce colic spit-up burping and gas.Sampler Kit includes 1 8oz bottle 1 4oz bottle 2 extra Level Two nipples and 1 cleaning brush Patented internal vent system created by Dr. Craig Brown BPA free Fits all levels of existing Dr. Brown s Standard nipples. Made in USA.