The keyboard has a membrane underneath that provides cushion like support. This was first discovered by a private company iFixit. The company discovered a thin silicone membrane covers the problematic butterfly mechanism under the keyboard providing protection against dust and dirt. An Apple patent claimed similar mechanisms for keyboard protection.
Website MacRumors fortunately managed to dig out an internal document where the Cupertino based giant has confirmed that the third-generation keyboard in 2018 MacBook Pro models are fitted with a membrane. The main function of the membrane is to “prevent debris from entering the butterfly mechanism”. The Service Readiness Guide for MacBook Pro that has been distributed to Apple Authorized Service Providers find such mentions.
“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.”
The United States version of the Service Provider guide doesn’t refer to this padding membrane. However, it does contain a link to a separate internal document that cautions against tearing of this membrane, as that would require “a top case replacement”.