iFixit:

The 2018 MacBook Pro keyboard is a wealth of secrets—it just keeps surprising us. Just when we think we’ve exhausted one vein of tasty tech ore, we find something new. And today, we bring this trove to you.

And:

We pumped this keyboard full of particulates to test our ingress-proofing theory. We started with a fine, powdered paint additive to add a bit of color and enable finer tracking (thanks for the tip, Dan!). Lo and behold, the dust is safely sequestered at the edges of the membrane, leaving the mechanism fairly sheltered. The holes in the membrane allow the keycap clips to pass through, but are covered by the cap itself, blocking dust ingress.

And:

On the 2018 keyboard, with the addition of more particulate and some aggressive typing, the dust eventually penetrates under the sheltered clips, and gets on top of the switch—so the ingress-proofing isn’t foolproof just yet.

I do appreciate the testing, good to know the threshold at work here. Bottom line, don’t dump a bunch of powder or sand on your keyboard and you should be fine.

If you want a more traditional, picture-laden keyboard teardown, iFixit has that too.

And on a related note, here’s John Gruber’s take on the legal/marketing side of the new keyboard, and the quieter vs. better at keeping out debris language.