In an internal document distributed to Apple Authorized Service Providers via multiple reliable sources, Apple has confirmed that the third-generation keyboard on 2018 MacBook Pro models is equipped with a “membrane” to “prevent debris from entering the butterfly mechanism.”
A segment of Apple’s internal 2018 MacBook Pro Service Readiness Guide describes the updated keyboard architecture as follows:
Keyboard and Keycaps
The keyboard has a membrane under the keycaps to prevent debris from entering the butterfly mechanism. The procedure for the space bar replacement has also changed from the previous model. Repair documentation and service videos will be available when keycap parts begin shipping.
While the U.S. version of the Service Readiness Guide does not specifically mention the membrane, it describes the component in a separate internal document titled “Butterfly Mechanism Keycap Replacement MacBook Pro (2018)”:
Caution: The keyboard has a membrane under the keycaps to prevent debris from entering the butterfly mechanism. Be careful not to tear the membrane. A torn membrane will result in a top case replacement.
Stay tuned for additional details as they become available.
Via The Mac Observer and MacRumors