PRODUCT DESCRIPTION Whether you're storing, traveling, or warming bottles of milk, Dr. Brown's Storage/Travel Caps keep your baby's meals safe. Designed to fit Dr. Brown's Options+ Narrow bottles - simply remove the nipple, collar, and internal vent system from the bottle, then screw on the cap to store milk. The storage/travel cap is leak-proof and keeps breast milk, formula, and other liquids safe and fresh in the refrigerator, portable coolers, and even airplane carry-on bags. When flying, remove the nipple, collar, and internal vent system from the Options+ bottle and replace with a storage cap to help prevent leaks caused by cabin pressure changes. Fully reusable and dishwasher (top rack) and sterilizer safe. BPA-Free. FROM THE MANUFACTURER These Storage/Travel Caps are designed for the standard 4-ounce and 8-ounce Dr. Brown's Natural Flow baby bottles. These caps securely seal the standard 4-ounce and 8-ounce Dr. Brown's Natural Flow baby bottles for travel and storage of formula or breast milk.