Medela's Wide Base Travel Cap for Breastmilk Bottles snaps into place on top of the bottle collar, preventing spills by covering the bottle nipple. This is the same travel cap that is included with all Medela Breastmilk bottle Sets. It is BPA-free, dishwasher safe, and microwave safe. The Wide Base Travel Cap is designed to be used only with other wide base parts: the Wide Base Collar (#2001485), the Wide Base Disc (#8107184), and Wide Nipples (#87133 or #87134). All wide base parts ARE compatible with ALL types of Medela breastmilk bottles, but ARE NOT compatible with older styles of collars, caps, nipples, and discs. For a better value on bottle accessories, check out the Breastmilk Bottle Spare Parts Kit (below)!