Compatible with all Medela breast milk bottles: Natural feel and shape Easy cleaning: Nipples may be cleaned in the dishwasher, Micro-Steamed, boiled or washed by hand Can only be used with wide base collars: Medela breast milk bottles come with wide base collars. Replacement collars are sold separately in our breast milk bottle spare parts set below Made without BPA: All parts that come into contact with breast milk are not made with BPA