https://www.theverge.com/circuitbreaker/2018/7/19/17590100/apple-macbook-pro-keyboard-membrane-dust-problem-fix-leaked

A recently leaked Apple service document obtained by MacRumors confirms what many already suspected: the newly introduced silicone membranes discovered by iFixit that are beneath the keycaps on the new MacBook Pro keyboard aren’t just there to muffle sound. They’re also there as a protective layer to block dust and debris from interfering with the sensitive butterfly mechanism that has proved so problematic for some users.

When Apple announced its latest MacBook Pro updates last week, one of the more notable changes to the hardware was a third-generation version of the much-maligned butterfly keyboard. But Apple insisted that the only real difference was that the updated models were quieter.